Getting activation code for an old Turbotax

I need activation code for 2020 for an amendment

 

When I tried to install it, it tells me that all available activations have been used. I guess because over the years I installed 2020 in different computers for the purpose of checking my old taxes and compare them to the new ones.

 

Where can I get or buy a code just to use it once more for this ammendment?