My first attempt was also not successful, but after my second attempt I was able to repair (the most) devices.
For all other interested users, these are the steps I did and what problems I still had:
- Backup created from HP19
- HP19 unplugged
- Performed factory reset on HP23 via USB tool
- HP23 unplugged
- USB Tool restarted and FW v10.0.4-rc.10 installed
- HP23 unplugged
- after a few minutes connected the HP23 to the power supply (I don’t have an ethernet adapter!)
- waited about 15 minutes
- migrated HP23 from the last HP19 backup
- waited about 15 minutes
- started repairing the Zigbee repeater
Nevertheless there were always problems with repairing some Zigbee devices, e.g.:
- An error occurred when pairing this device again. Please try again.
- This device could not be repaired. The device that joined the Zigbee network is not the device you are repairing.
- Device is added…
This seems to take too long. Try turning your device off and on again. If the device is battery powered, press a button to reactivate it.When I once called Developer Tools → Zigbee, the following error message also appeared 1x:
- Zigbee is busy, please try again later.
Also, when I tried to repair a device, it left the Zigbee network. 2x I had to restart the HP23 as well, so that I could repair more Zigbee devices at all.
(Source, quickly translated with deepl.com 
)
So Athom has still to do a lot of homework.
However, I would also mention that the Zigbee devices are now working properly and are stable.
