How do I claim on my 2019 tax return monies that I over paid the IRS for tax year 2018.

Federal taxes paid or refunds of the same are not entered anywhere on a federal income tax return.  There are a couple of state's that will allow the deduction ... look for that in the state interview if your state allows it.

When you filed 2018 did you apply the refund to 2019?  Did you enter it on 1040 line 21?  

If it didn't transfer over from last year then enter a refund from last year that you applied to this year here.   BUT first make sure it's not already there.  You don't want to apply it twice.

Federal on left

Deductions and Credits at top

Then scroll way down to Estimates and Other Taxes Paid

Other Income Taxes - Click the Start or Revisit

Next page scroll down to 2018 Refund Applied to 2019

Click Start or Update by the tax you applied