I made 2 copies of a filed return but I can't modify or delete the copies. How do I delete or modify a mere copy made of a return previously filed?

Unfortunately, you can't. If one makes a copy of a "locked" return, the lock copies over too. We're working on removing the lock on a copy, but there's currently no scheduled release date for this enhancement.

Are you attempting to edit the copy because you want to file an adjustment? If so, here's how you file an adjustment: https://turbotax.community.intuit.ca/replies/2647992

An additional bug in this workflow after you make the copy - the _original Netfiled return in the Return Manager wrongly gets a 'Trash' icon beside it. This original return you filed should not be deletable.

Thanks @tojontr. I believe that if you select the trash can, TurboTax won't actually let you delete a filed file.
The trash can shouldn't show, but it's a cosmetic defect that we're working on.

I agree, I assumed that was the case, but I wasn't about to test the theory on my Netfiled return 🙂