Question: what is the largest city the country that is a natural boundary between the country that hosted the tournament and the country That Dam is located?

Knowledge 1: That Dam
That Dam (Lao ທາດດຳ, meaning Black Stupa) is a large stupa located in Vientiane, Laos. Many Laotians believe it is inhabited by a seven-headed nāga who tried to protect them from an invasion by the Siamese army in 1827. [SEP] Knowledge 2: Thailand
Thailand (/ ˈtaɪlænd / TY - land), officially the Kingdom of Thailand and formerly known as Siam (until 1939 and again from 1946 to 1948), is a country at the centre of the Indochinese peninsula in Southeast Asia. It is bordered to the north by Myanmar and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the west by the Andaman Sea and the southern extremity of Myanmar. Its maritime boundaries include Vietnam in the Gulf of Thailand to the southeast, and Indonesia and India on the Andaman Sea to the southwest. The capital and largest city is Bangkok. With around 69 million people, Thailand is the 20th-most - populous country in the world. [SEP] Knowledge 3: 2020 AFC U-23 Championship qualification
Of the 47 AFC member associations, a total of 44 teams entered the competition. The final tournament hosts Thailand decided to participate in qualification despite having automatically qualified for the final tournament. [SEP] Knowledge 4: Geography of Myanmar
Myanmar (also known as Burma) is the northwestern-most country of mainland Southeast Asia, bordering China, India, Bangladesh, Thailand and Laos. It lies along the Indian and Eurasian Plates, to the southeast of the Himalayas. To its west is the Bay of Bengal and to its south is the Andaman Sea. It is strategically located near major Indian Ocean shipping lanes.
Knowledge 1: That Dam
That Dam (Lao ທາດດຳ, meaning Black Stupa) is a large stupa located in Vientiane, Laos. Many Laotians believe it is inhabited by a seven-headed nāga who tried to protect them from an invasion by the Siamese army in 1827. [SEP] Knowledge 2: Thailand
Thailand (/ ˈtaɪlænd / TY - land), officially the Kingdom of Thailand and formerly known as Siam (until 1939 and again from 1946 to 1948), is a country at the centre of the Indochinese peninsula in Southeast Asia. It is bordered to the north by Myanmar and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the west by the Andaman Sea and the southern extremity of Myanmar. Its maritime boundaries include Vietnam in the Gulf of Thailand to the southeast, and Indonesia and India on the Andaman Sea to the southwest. The capital and largest city is Bangkok. With around 69 million people, Thailand is the 20th-most - populous country in the world. [SEP] Knowledge 3: 2020 AFC U-23 Championship qualification
Of the 47 AFC member associations, a total of 44 teams entered the competition. The final tournament hosts Thailand decided to participate in qualification despite having automatically qualified for the final tournament. [SEP] Knowledge 4: Myanmar
Myanmar (myan-MAR i/miɑːnˈmɑːr/ mee-ahn-MAR, /miˈɛnmɑːr/ mee-EN-mar or /maɪˈænmɑːr/ my-AN-mar (also with the stress on first syllable); Burmese pronunciation: [mjəmà]),[nb 1] officially the Republic of the Union of Myanmar and also known as Burma, is a sovereign state in Southeast Asia bordered by Bangladesh, India, China, Laos and Thailand. One-third of Myanmar's total perimeter of 1,930 km (1,200 miles) forms an uninterrupted coastline along the Bay of Bengal and the Andaman Sea. The country's 2014 census revealed a much lower population than expected, with 51 million people recorded. Myanmar is 676,578 square kilometres (261,227 sq mi) in size. Its capital city is Naypyidaw and its largest city is Yangon (Rangoon).
Knowledge 1: That Dam
That Dam (Lao ທາດດຳ, meaning Black Stupa) is a large stupa located in Vientiane, Laos. Many Laotians believe it is inhabited by a seven-headed nāga who tried to protect them from an invasion by the Siamese army in 1827. [SEP] Knowledge 2: Thailand
Thailand (/ ˈtaɪlænd / TY - land), officially the Kingdom of Thailand and formerly known as Siam, is a country at the center of the Southeast Asian Indochinese peninsula composed of 76 provinces. At 513,120 km (198,120 sq mi) and over 68 million people, Thailand is the world's 50th largest country by total area and the 21st-most - populous country. The capital and largest city is Bangkok, a special administrative area. Thailand is bordered to the north by Myanmar and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the west by the Andaman Sea and the southern extremity of Myanmar. Its maritime boundaries include Vietnam in the Gulf of Thailand to the southeast, and Indonesia and India on the Andaman Sea to the southwest. Although nominally a constitutional monarchy and parliamentary democracy, the most recent coup in 2014 established a de facto military dictatorship. [SEP] Knowledge 3: 2020 AFC U-23 Championship qualification
Of the 47 AFC member associations, a total of 44 teams entered the competition. The final tournament hosts Thailand decided to participate in qualification despite having automatically qualified for the final tournament. [SEP] Knowledge 4: Geography of Myanmar
Myanmar (also known as Burma) is the northwestern-most country of mainland Southeast Asia, bordering China, India, Bangladesh, Thailand and Laos. It lies along the Indian and Eurasian Plates, to the southeast of the Himalayas. To its west is the Bay of Bengal and to its south is the Andaman Sea. It is strategically located near major Indian Ocean shipping lanes.

Answer: largest city is Yangon (Rangoon)