You can try retopology addons that re-topologize it for you (I haven’t used those tho).
Or what I do: I learned/still learning face and muscle topology aka good edge-flow. Good topology is important if you want to rig it:
Start with the 6th video in the playlist.
(Even just studying the pics and where each colour flows into might be enough).
It took me quite a lot of practice to get semi-confident with this.
You can also look at your own face in the mirror in a well-lit area while making exaggerated face expressions, seeing how the muscles on your face look.
EDIT: You’ll probably have to learn weight-painting if your mesh deforms weirdly after being rigged to an armature.
Good luck!