Rectification return for AY 2019-20

Hello,

An individual who was working in india from april 18 to dec 18 and later went to UK for job for next 3 months. and he has filed his original return and have taken refund for the taxes, without showing nri income as taxable and the return processed and now can't revise it for paying the taxes on nri income as he was resident hus global income will be taxable.


Now my question is
1. can he pay the taxes on foreign income with interest now and file everything properly in rectification return?
2. if yes, then how to adjust that refunded amount, do he have to pay it back to the government or what will be the right way?

Thanks