How do I amend my 2020 tax return? I got a 1099-INT in the mail after filing my taxes for the year.

I got a 1099-INT in the mail, how do I amend my taxes? Also, I got a 1095-C and I never asked for coverage under my employer and as such do not get coverage. Do I need to amend that to my taxes? My return was already accepted by the IRS.