How to tuck shirts in?

So basically, I'm editing a base game mesh to practice making cc. I've previously made recolors, but this is my first time tweaking the original mesh. I cropped a shirt, but I would like for it to tuck in with high wasted skirts and pants. The original mesh wasn't one of those that automatically tucks in, so now it just clips a little. Not badly though and I could live with it clipping a little, but I want to learn more so that some day I can try to make my own meshes some day. So, how to proceed? I couldn't find a tutorial about it anywhere, so I'm posting here.

Thanks in advance!