You can write the actual real date when you moved abroad. Example: You left India on 1 Jan 2020 to study in the USA. You traveled back to India temporarily for 2 months to spend with family from 1 April 2021 to 30 May 2021. You then returned back to the USA to continue your studies. You should write the date of leaving India as 1 Jan 2020. Note that if you have changed the address while staying abroad, this date should be the date you started living at your current residential address.