After you file

In the past you had to download the full program to amend on Mac.  You have to call in and ask for it.

 

Contact Customer Service
5am-5pm Pacific Time (8-8 Eastern) Every Day until Oct 25, 2019
And until 9pm (12 midnight Eastern) on Tue 10/15/19
https://support.turbotax.intuit.com/contact/