You will get a 1099R for the RMD. You enter that exactly as shown including any withholding taken out of the RMD.
Then if you send in an Estimated payment directly to the IRS yourself you enter that separately. You don't have to indicate you used the RMD to pay it.
You can type estimates paid in the search box at the top of your return and click Find and it will give you a link to Jump To it.
OR
To enter Federal or State Estimated Taxes Paid, including a state estimated payment made in January for the prior year, go to
Federal on left or at top. Personal (Home & Business)
Deductions and Credits at top
Then scroll way down to Estimates and Other Taxes Paid
Estimated Taxes - click the Start or Update button
Estimates paid will be on Schedule 5 line 66 which goes to 1040 line 17.
