For On-Line version
You appear to be using the TTax On-Line version. Unfortunately the on-line version does not support a 'what-if' scenario (that is only available with the desktop version).
Once you make ANY changes to the online version the previous information is overwritten and is PERMANENTLY deleted. You will have to manually re-enter/re-create your return.
You might want to try to create NEW dummy accounts for your various scenarios and then simply abandon them when you are finished.
Create New On-Line account:
turbotax.com and look for the 'New to TurboTax?" 'Start for Free' BLUE button near the top center of the screen.
I have an idea ... you could amend the return then delete the amended return so you don't mess up the archive ...How do I amend my 2018 TurboTax Online return?
How do I cancel or undo an amended return in TurboTax Online?
If you started amending your tax return by accident and would like to cancel the amendment:
1. Open your return if it’s not already open.
2. In the left menu select Cancel amend.
3. Select Yes, I want to cancel my amended return.