Foreign tax credit carryback -- how do I enter this in TurboTax? (It only asks about carryovers)

For 2018, I filled out form 1116 and the worksheet limit for my foreign tax credit was well below the credit I could claim. For 2019, I filled out form 1116 and had a few hundred dollars in foreign tax credit that I couldn't use because it was over the calculated worksheet limit. I've read I can amend my 2018 return to do a carryback to 2018 (and I'll still be under my 2018 worksheet limit).

 

Can this be done in TurboTax online by amending my 2018 return? If so, how do I enter it?

 

While amending my 2018 return in TurboTax Online, I only saw a place to enter carryovers from 2017 and earlier (not a carryback from 2019) when I went through the foreign tax credit section of TurboTax.