I have this model with separate meshes for the eye area and the rest of the head. I wanna merge the eye UV map to the head, the head UV map has an open area around the eyes, which is where the eye UV map belongs, but I don’t know how to merge them correctly.
I have tried simply doing Ctrl+J but it just does this
I tried renaming the UV maps to be the same which kinda fixed it, but not what I wanted, the UV maps were still on separate textures.
Is there a way I can copy the eye’s UV map in the UV editor and paste it into the head’s UV map area?
You did that by renaming UV maps to make them called the same and joining objects afterwards. UV coordinates of both meshes will be included into one UV map.
To make that result usable it’s often required to bring UV islands to the same scale (also called texel density, in default Blender can be done by going to header > UV > Average Islands Scale which was Ctrl+A in the UV editor in Blender 2.79 but since 2.8 the command is no longer assigned to any) and then pack UV islands to avoid any intersections in the UV map.
Looks like those meshes are assigned to different materials while both of materials have different images added in the material node setup. For your convenience images are shown according to materials’ node setup they belong to. Try to remove image in the UV editor by clicking X button in the UV editor header (that won’t remove it from material setup) and then click Pin button next to the X button. That pin will make current background UV editor image (or lack of it) display regardless of mesh you selected.
Note this doesn’t do anything to UV coordinates; this way they are shown on the same background image but they are included into one UV map anyway. This is just displaying option.