Mesh Issues (Solved)

Hey! Always share package and blend file while asking for help, now I can help only basing on pictures you added.
Form what I see you need to retransfer uv_1 cause it's messed. Use dress similar to your in shape and length. Before transfering uv_1 or weights separate body parts from dress so you do not transfer to them. While transfering uv_1 use this settings

Before transfering weights, uv_1 or vertex paint you need to select body parts, then press P - Separate so they are separated from dress and you transfer only do dress, not body parts
You need to search for better reference mesh, I used base game maxi dress cause I had already this mesh exported and this is difference between my and your uv_1 (your on top, my bottom)

Transfer weights from more suitable reference too (definitely a dress, not legs). After transfering weights use options: Clean (All Groups) and Limit Total (Limit to 4) (You can find them on the list above Weights Transfer Button in Weights menu)
Bottom part of dress should be vertex paint in a different color, cause dress move differently than legs. Select your dress from the bottom to smowhere in the middle of pelvis bone. Then in vertex paint choose option "Face selection masking for painting" (cube with one red side), choose 3FFF00 color and Paint -> Set Vertex Colors. Then uncheck Face selection and use Paint -> Smooth Vertex Colors
You should move your dress further form legs too, cause it's too thick for this kind of mesh (with legs under dress).
It still gives me some jagged look on bottom while walking, I think it's because your uv is too dense compared to ea ones, but it's softer than one you had.