Well I spent bloody ages, on several occasions too, looking for how to make my wireless doorbell push switch unit work with the chime part after changing the batteries! It seems they lose their pairing information instantly and so need to be paired in some way.
I tried to guess the method, and as it happens guessed right, but it didn’t work as the battery in the bell push was too low too, not just the chime unit batteries I had changed. At least when you know the real method, that leaves fewer variables when it doesn’t work!
So here are PDFs of the instructions which I accidentally found again after months of not having a doorbell! Copyright Siemens of course. But if they can’t be bothered to make them available then I will! Hope they’re useful, please leave a comment.
There’s a lot to be said for old-fashioned wired doorbells.