Where do we enter the tax amount we already paid in 2023 for 2024?

If this occurred in 2024 then you should have received a Form 1099-R.  On the 1099-R any federal income taxes withheld will be entered in box 4 of the form.  The taxes withheld flow to the 2024 federal tax return, Form 1040 Line 25b.

To enter, edit or delete a form 1099-R -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On IRA, 401(k), Pension Plan Withdrawals (1099-R), click the start or update button

Or enter 1099-r in the Search box located in the upper right of the program screen. Click on Jump to 1099-R

Online editions -

On the screen Did you get a 1099-R in 2024? Click on Yes

On the screen Let's import your tax info Click on Change how I enter my form
On the screen How do you want to add your 1099‑R? Click on Type it in myself

On the screen Who gave you a 1099-R? select the type of 1099-R you received and Continue

What does 2023 have to do with it?  If you converted to a ROTH IRA in 2024 you should have a 1099R for it.  The tax withholding is in box 4.  Or what/how did you pay the 2023 tax at the beginning of 2924?

Enter a 1099R under
Federal Taxes
Wages & Income
Then scroll way down to Retirement Plans and Social Security
Then IRA, 401(k), Pension Plan Withdrawals (1099-R) – Click Start