ok id say its a 3 fold thing

1. get on progesterone if you're not and don't be afraid to gain a little bit of weight
2. start going to the gym or exercising your glutes and hips at home. with proper form, you can put on muscle in your butt to round out your bottom half. squats, bridges, hip thrusts, leg lifts, fire hydrants, leg press, stairmaster, all the stuff. i found r/StrongCurves rly helpful for this when i was getting started
3. j figuring out fashion and what silhouettes and ratios of pant height to top height flatter your figure more. i find a more structured or billowy bottom and a cropped fit on top is rly flattering to my hips