Login to your profile at oculus.com and check out My Security Center and then the sessions option, and log out of all sessions, this will render the stolen quest useless because you have to log back into your account via the android app, then connect to the quest via the app to get it back working again.
I'd definitely contact support as they will be able to ban the quest's from connecting to their servers.
I just did it for my own quest and it takes away the quest hud, all you can do is look around the environment
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