Updating Watch OS and/or pairing fails with a new display

After installing a display from another watch I can’t upgrade watch OS 5 to 6. Than I want to reset the watch to pair it once again with my iPhone and it doesn’t work anymore. Any tipps what I can do? :(

I found the solution:

the watch must be on watchOS 5 to accept the new display from another watch.

If it fails to update, you have to connect the two cables left and in the middle on the new screen and the right (for NFC/GPS) with the old screen (you must have the old screen!!!) and then pairing and updating will finish!

After the update you can disconnect the old screen and connect the right cable to the new screen.

Re-pairing and updating isn‘t an issue anymore, but if you want to use Apple Pay, the NFC Chip must be replaced with the one from the original screen.