You can make 2020 estimated federal tax payment using the IRS payment website - https://www.irs.gov/payments

You can also use IRS Form 1040-ES to mail a payment to the IRS for tax year 2020 - https://www.irs.gov/pub/irs-pdf/f1040es.pdf

You can mail a check payable to "US Treasury"

write your SSN, phone number and "For 1040 year 2020" on the check.

Note that your check will go to the bottom of the pile of unopened checks already mailed to the IRS.