How do I avoid getting a previously paid refund amount in addition to the new amount due me on an amended return?

The refund from the original return should be entered on line 18 of the Form 1040X.Then it gets subtracted from the total refund. Line 21 of Form 1040X should show just the additional refund. If you correctly followed the instructions for amending your return this will happen automatically.

Go to the following link for instructions to amend a tax return that you filed with TurboTax.

https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed

If you need further help, tell us what year you are amending.