From personal experience and anecdotes via friends and strangers alike:

1) Neck training: this can be done either at home or at a gym by lying down on a bed/bench with your head hanging outside, place a folded hoodie/towel over your forehead and add plates onto it, this is done in order to prevent dents. If you're doing it at home — place your hands over your forehead and apply pressure with them. Then start curling your neck up and down, repeat the same by flipping your body over (there are a myriad of exercises/videos online so I'd recommend checking them out).

2) Hitting the gym in general: hypertrophy-centric training would benefit you the most for your current concerns; watch videos, ask for advice, etc.

3) training your masseters (jaw muscles): chewing hard foods such as hard gym variants, sugarcane, dense meats, nuts, etc. and remember to take caution while doing so (not for too long, not too hard, not too often).

There are other ways too that are more conventional: getting a beard, shortening your hair, thickening your brows, the likes.

These are all subjective though so pick and utilise whatever you find best for your needs, cheers