Conversation so far:
Who led the Sinhalese People?
Prince Vijaya and his 700 followers left Suppāraka, landed on the island at a site believed by historians to be near modern-day Mannar, and founded the Kingdom of Tambapanni.
Who else was the leader of the Sinhalese People?
The elected minister of the people Upatissa, the Chief government minister or prime minister and leading chief among the Sinhalese became regent and acted as regent for a year.
What was the new capital by Upatissa called?
While he was king, Upatissa established the new capital Upatissa, in which the kingdom was moved to from the Kingdom of Tambapanni.
Where did the Sinhalese People travel to after moving to the new capital Upatissa?
When Vijaya's letter arrived, Sumitta had already succeeded his father as king of his country, and so he sent his son Panduvasdeva to rule Upatissa Nuwara.

Question: Where did they go next?
Self-contained rewrite: Where did the Sinhalese People go after Upatissa Nuwarra?