Problem with clothing and moving in blender

Hi all. I’m new in blender, so I have faced very annoying thing. So the thing is that I made a body of human, I made clothes, I have joined them together with function “join”(ctl+j). I made metarig and it kinda works (I joined body with rig with ctrl+p auto-weighted), but there’s one problem. When I move one of my human’s leg shorts are staying in the same position and not moving. The rest of the clothing is ok. Only shorts.

The question is what can I do? I know that i’ve probably made many mistakes and that’s why this is happening, but maby I can do something now that could fix this? I’ve watched every single video on youtube, nothing helps. Thanks in advance guys.