Open your band from Bands and scroll to Your band's data.
To back up: press Download my band's data. You get a ZIP of spreadsheets: band settings, players, venues, gigs, offers, songs, set lists, lending, kits and pay. It holds contact details, so keep it somewhere private. It has no passwords or sign-in links. Chart files are not in it, so keep your own copies.
To restore:
Restoring adds what's missing and updates what matches (players by email, gigs by date and title). It deletes nothing and sends no email. If you wait too long on the preview, choose the file again.
The site also keeps its own nightly copy.