A coach can send the program invitation to a past client again, as if they were a new client, or the client can go to their 'past programs' and resubscribe to previous program subscriptions there.
If the past program a client is currently cancelled to is a Fixed Length 'type' please let FITR support team know the client's email first. We'll need to remove it from a master 'blocked' list, since Fixed Length programs are ordinarily designed to be retained by clients after they've signed up.