I use procreate and blender. Procreate is the program ive been using for longest and know well, it also supports 3d so its easy to see if there are any visible seams on the texture (just the 2d part works with nay other graphics software one you are familiar with). First i selected the blank underwear area and made it into a separate layer. Then its just colorpicking and matching the texture of the original texture with a bunch of eheh textured brushes on a clipping mask until blends. And then i converted it in blender with dds addon, in my experience it offers better export options and doesn't turn certain textures "blocky" like Paint.net does :)
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