How do I add a second hand player to my Squeezebox account?

I've bought a Liv Zen (former Innuos product) and I can't get Tidal to work in HD. It works fine on my RPi. After trying everything, I've worked out that is probably because the RPi is registered on My Squeezebox account but the Zen won't. The Zen was registered on another account and the seller will not respond to messages.

My question is, who can I ask to transfer the Zen to my Squeezebox account? I think I know the email of the previous user's account.

Thanks in advance.