my characters face keeps returning to the orginal position when i use a blendshape which in turn deforms the characters typoligy.

i already rigged the body and head together before creating the blendshapes and then extracted the head from the body and afterwards combined them again, and i dont want to go back and redo everything again. so i was wondering if someone else had this same problem and how they changed the outcome?

please respond as soon as possible