There are 2 answers to your question, depending on if you use the On-Line version of TTax or if you use the Desktop version (which is installed on your computer). Hint: Desktop version gives you more flexibility and options.
For DESKTOP version ONLY
Select 'Forms Mode' - (upper right corner of Step-by-Step screen)
Select 'Open Form' - (upper LEFT corner (just above "Forms in My Return" click on icon)
Enter "What-if" (without quotes) in the Search field (at top under 'Search or Browse ,,,' heading)
'Double Click' on the "What-if" entry listed in the list of forms below (under 'US Form 1040 ...')
NOTE: Be sure to type the search phrase SLOWLY, and to use a '-' and not a space between the words entered. The search will auto-complete generally by the time 'wh' is entered.
For safety, to protect your return, whenever you are doing things like a 'what-if' compare, it is a good practice to make a COPY of your return and do the 'what-if' exercise on the COPY.
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.
How to Clear AND Delete
How to clear an on-line return and start over
https://ttlc.intuit.com/questions/1900891-how-do-i-start-over-in-turbotax-online
(Please note that the link may 'appear' to be truncated, however it will
work (if you hover your mouse over the link you will see the full link.)
How to delete tax return in TTax On-line
https://ttlc.intuit.com/questions/1899886-can-i-delete-my-tax-return-in-turbotax-online
(Please note that the link may 'appear' to be truncated, however it will
work (if you hover your mouse over the link you will see the full link.)
Note: This will also clear/delete and data your have transferred from last year or downloaded from a Financial Institution.
CAVEAT:
While you can clear the information in a return in an account, you CANNOT delete an account.
If you still want to use TTax On-Line, TurboTax's TaxCaster may be of some help
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
