I am going to submit my app to App Store and it finds invalid toolchain .
New apps and app updates must be built with the public (GM) versions. Xcode 9 or later.
Should I reinstall Xcode 10 GM directly instead of beta?
Yes, you must use a stable release of Xcode to submit a build to App Store:
i.e. the versions in bold from this unofficial list: https://xcodereleases.com/
Beta versions of Xcode are only good for TestFlight builds, not App Store builds.
Not also that there is a minimum Xcode version depending on your product platform (iOS, tvOS, macOS): https://help.apple.com/app-store-connect/#/devb1c185036