Can't reset an old homey pro 2019, just endless loop

Yeah that’s the odd part, you’re not the only one confused: You’ll have to add a “new” Homey, in order to be able to connect to your owned Homey which is in recovery mode.
In the end, no new Homey is added, you’re just having your owned Homey available in the app again.

Maybe this part of the howto is not clear enough?

Are you willing you improve this text?