how do I toggle between two individuals to complete tax filings

Are you using the desktop version?  If so, you simply select 

1. File up in the upper left hand corner of the screen
2. Open Tax Return
3. Save the return
4. Select the other return you want to open.  

You cannot have them both open at the same time.

If you are using the online version, you would need to have 2 screens open, one in incognito and switch back and forth.  Or you can log in and out of the returns to go back and forth. 

Why are you trying to "toggle" between two tax returns at once?   Why not work on them one at a time?  

If you are using online software --- which is what you are posting from--- each return needs its own account and user ID.   If you use the same account and user ID for two returns, the first one will be overwritten by the second one and will be lost forever.  You get one return per fee when you use online TurboTax.