Back to El Capitan
I installed the test version of Sierra. It is terrible. Can I get back to El Capitan?
I do not know enough about the problems to present them to Apple but had an extra computer and thought I would try the new S/W.
you can restore your computer from a time machine backup if you made one as recommended by the beta installer
Use Time Machine to back up or restore your Mac - Apple Support
if you do not have any backup and you only have the one HD you will need to restore your original OS from recovery mode or the disks that shipped with your computer depending on the age
