Ideally, the previous owner should deregister the H9 in the app before sending it to you. There's a function to do so in the pedal settings screen, and it's quick and easy. If you already have the H9, you can just send an email to email@example.com and we'll take care of it for you.
You won't have any trouble getting the Resonator algorithm. It's free for every registered H9 user through the end of the year.