How do I undo the upgrade? I just need basic free tax return

You cannot use TT Free if you have a 1099-G, as you indicated in your other post.

https://ttlc.intuit.com/questions/4693180-i-mistakenly-chose-tax-grant-then-was-prompted-to-upgrade-...

If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over with a lower priced edition.  Click on Tax Tools on the left side of the program screen while working on the 2018 online tax return.  Click on Clear & Start Over.