State estimates are entered on the same Tax Payments Worksheet as federal estimates.  I'm curious about you wanting to enter 2021 estimate already paid.   Are you referring to Jan2021 payment for the 2020 tax return or April2021 payment for 2021 return?    If for the 2021 return, you do not enter it anywhere in the 2020 tax program.  You will need to wait to enter in the 2021 program