Osram Lightify Switch - Factory reset without old Lightify Gateway

[heikoh81]

Hello,

from my old Lightify setup I have 5 Lightiy Switches, similar to this Smart+ Switch:
https://www.zigbee2mqtt.io/devices/4058075816459.html

2 are factory new and could be added to zigbee2mqtt without any problems.
3 were paired to an old Lightiy bridge before, which I don't have any more.
I read on the internet somewhere to be able to repair these 3 switches, you first have to remove them within the old lightiy app, then hold 2 buttons for 3 seconds, and then they can be paired to another bridge again.

As I don't have to old app and the old gateway anymore, this is not an option.
Has anyone found a way to factory reset these switches without the app and the old gateway?
Holding down the upper left and bottom right button for > 10 seconds as suggested in the manual does a "factory reset", however, pairing to another bridge is still not possible.

Would be a shame to throw these 3 remotes to trash, so maybe someone has a hint for me.
Thanks, greetings,
Heiko