Sorry, for improvements installed in 2018, TurboTax has not yet been updated to allow you to file an amended return. The program update is scheduled for mid May. It was delayed because there were so many tax law changes that had to be processed for 2019, and then more changes that had to be processed for the coronavirus emergency.
(improvements made in 2019 can be claimed on your 2019 tax return. That software is ready.)
