I need to do my uncles taxes for him. Every time I sign in to turbo tax it takes me to the return I completed for my mother. How do I get back to a different return?

A TurboTax Online account can only be used for one tax return. You cannot do your uncle's tax return with the same account that you used for your mother. If you need to file another tax return for someone else you have to use a different account. You can have up to 5 TurboTax Online accounts with the same email address.

You can start another return in TurboTax Online by:
Logging out if you are in your account
Choose what TurboTax Online product you want to use for the second return
https://turbotax.intuit.com/personal-taxes/compare/online

Create your account screen
Set up a new login for the second return
Start working on the new return