Sorry you have to clear and start over to downgrade.
Or If you want to use a lower version, one thing you can do is move your Online file to a lower Desktop program and continue without paying for Online or needing to reenter your info. All the Desktop programs have the same forms. You just get more help and guidance in the higher versions.
To continue in the desktop version see this…….
https://ttlc.intuit.com/community/choosing-a-product/help/how-do-i-switch-from-turbotax-online-to-the-turbotax-software/00/26129