then you click the genital mesh then the body mesh and join the object ctrl+j, and then in edit mode, reconnect all the faces so that you patch the genital mesh into the body mesh. with that you can then finish and delete the remaining vertexes so that the area for the genitals is clear. With the body mesh, delet all the vertexes that exactly match where the edge of the genital mesh is. But that doesn't really work well in blender, so we'll just have to transfer the image to the high quality mesh and blend them together using fancy shader nodes. The reason for this is because the lower res mesh is meant to use a new image that holds the texture for the genitals, covering up the other mesh. Usually what I have to do is, selecting the two genital meshes, I have to transfer the uv map from the low res mesh to the high res mesh (though you may have to select things backwards just due to how the transfer uv command works in blender).

What Rich said is right, usually what happens with importing into blender is, since the genitals are geograph, meaning they just hide the original mesh and add a new one, what you are probably seeing is, a body mesh, and two genital mesh, one that matches the quality of the body, and other lower-resolution one that kinda floats away from the body.

Daz blender bridge