markd69 you mean downgrading Flarum ? I wouldn't recommend it.
You could re-install beta 7 by copying the previous Flarum skeleton via Composer or git, hard-coding the core and core extensions versions and installing via Composer. Then you also need to hard-code many third-party extension versions if they have received a beta 8 update.
Downgrading an existing install is even more complicated because you need to revert the database. While technically possible, I don't think any command allows you to rollback the correct migrations to go back to beta 7 in a user-friendly way. Also, some data might get lost in the process...