Downgrade to IOS 13

Delete the current public beta profile from settings then restart your phone. After that wait for the official release of iOS on September 24 and then you'll be brought out of beta.

Check this article for more help: https://beta.apple.com/sp/betaprogram/unenroll#ios

You cannot do that.

You have a beta and you have to wait till iOS 13.1 is officially released.