Yes, you can carryback the amount of unused Foreign Tax Credit to 2018. If that does not use all of the credit, you can then carry the rest of the credit forward for 10 years.
Foreign Tax Credit
You will need to amend your 2018 tax return to carryback the credit.
How to Amend Your Prior Years Tax Return Using TurboTax
Once you have made the changes to your return, you will need to print, sign, date and mail your amended return according to the instructions that print out with the return.
Amended returns cannot be efiled.
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