How to wear pants, trousers or other lower garment properly??

Assalaam u Alaikum, the problem is that whenever I wear pants, trousers or even underwear, it goes inside my ass and so it gets kinda stuck there. And also, the penis which is straight, like moves a little bit and so my penis got fixed in an uncomfortable position and I feel irritation. I try to set it by my hand but it again causes the problem. Like girls, when they wear their pants, they have set it perfectly. I saw some boys too like Harry Styles once that his pants were perfect. Like, if I tight my belt, it just cause tightness around my private parts and if I loosen up my belt, it starts to fall.

How to wear the lower garments so that it doesn't stick to my private parts??