How do I amend a 2018 return that I filed by mail? I've already received the refund

Did you use TurboTax to prepare your tax return?

Yes I did

I'm either doing something wrong or don't understand step 4.  I open my original return and then save it under a different name.  But now that I have the "new" file open, I can't find anything in the program that says "amend" or "jump to".  What am I misunderstanding or not doing correctly?

You can use your TurboTax software to prepare your amended tax return Form 1040X.   The link below has information on how to file an amended tax return.

https://ttlc.intuit.com/replies/3288565