Do you mean that it's not showing up on your IRS Online account? You will have to contact the IRS.
Taxpayers with account questions may call 800-829-4933.
Refer to the IRS website Your Online Account and Here’s how individual taxpayers can view their tax account info for more information.
If you mean you made an estimated tax payment, it does not automatically show up like withholding on a W-2. You enter it under Deductions and Credits, the Estimates and Other Taxes Paid Grouping in the Estimates section.