Restoring puts your boat back as it was when you made the backup.
It replaces everything on your boat, on all your devices. If the boat has anything on it, Ballast lists what will be deleted and asks first. This can’t be undone, so back up what’s there now if you might want it.
iPhone: tap your boat’s picture at the top left, tap •••, then Restore From Export….
iPad: open the tab with your boat’s name, tap •••, then Restore From Export….
Mac: choose File ▸ Restore From Export…
Then choose your backup.
Still stuck? Hail us.