changing the time on my old watch

hi. ive just bought a vintage pocket/ brooch watch. i was wondering if anyone could help me figure out how to work it, (ive never had one before)

its apparently swiss, imported to glasgow in 1915, its a wind up. but thats all i know, it is a small very pretty ladies watch, is silver and the front rim and the back are inset with tiny pearls.
ive taken the back off to change the time, but cant seem to be able to.
im hoping that the vintage watches are similar and someone will know how to do this.

thankyou for your time.