You need the form itself or you need to know where to enter it?
If you took a distribution from a retirement account in 2020 then the account administrator was required by law to get the 1099-R to you not later than Jan 31, 2021.
If it got lost somehow then contact the administrator of a copy.
If you have an online account with that retirement plan then it might be available online.
Then why do you need a 1099-R? If you received money form a retirement account then only you would know who sent it to you and what account you have.