Resident assessee's IT return ..only having foreign income

My brother went to Myanmar in 2016 on a job and stayed there until 2019 August. meanwhile every year used to come to India for less than 40 days every year.  in the year 2019-20 he permanently returned in the month of August2019 and joined no other job during the rest of the year.As a resident (RoR) he had received salary till August 19 and gratuity from the company who sent him to Myanmar.  He did not filied IT return for the assessment year 2020-21 thinking he has  no income in India. Now I think it's not possible to file the return for the assessment year 20-21. what is the remedy?