There are a few Buser movements on 17jewels.info and ranfft.de but none are an exact match.
This is similar in construction but a different shape. -> https://17jewels.info/movements/b/buser/buser-75/
Which suggests it may be a Buser movement, but beyond that, there is little information.
Thats a new one for me. It did find some movements maked as "Nidor" under the trade name of "Buser"
This is one of those watches that you will just have to repair without any manual/tech guidance. However I can not see any obvious way of letting down the mainspring which would be fatal for the watch without this first step.