For the NextGenSkin you should use Hanmens NextGenShader for best quality.
Open Material Editor (Body) in Body/Overall and search for the skin_body_00 and choose Hanmen/Next-Gen Body
View attachment 1740542
After that you have to do the same in Material Editor (Head) for skin_head-00.
If you don´t find Hanmen/Next-Gen Body and Face you don´t have this mod - as Sykosis said above this is a payable mod.
Therefore you can choose "AIT/Skin True" for Body and "AIT/Skin True Face" for the head (games default shaders).
But you don´t need to use Hanmen Tex, this is only the best Textures available.
You can choose another Skin Type, e.g. [hooh] 4K or the NYAACHO`s
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Maybe you have first to save your change and load again into creator to activate the new skin on your card.
By the way: if you have visible issues with your chars it´s always helpful to add a screenshot to your request!