A federal tax refund is not entered on a federal tax return.
Or are you asking about applying a 2019 federal tax refund to the 2020 federal tax return because you selected that option on your 2019 tax return.
How do I claim 2019 tax refund that was applied to 2020 tax return
To enter, change or delete a refund from the prior year applied to this years taxes (Federal, State, Local) -
Click on Federal Taxes (Personal using Home and Business)
Click on Deductions and Credits
Click on I'll choose what I work on (if shown)
Scroll down to Estimates and Other Taxes Paid
On Other Income Taxes, click on the start or update button
On the next screen select the options under 2019 Refund Applied to 2020
Or enter refund applied to this year in the Search box located in the upper right of the program screen. Click on Jump to refund applied to this year
The prior year refund amount applied is shown on Form 1040 Line 26