Fusing meshes into 1

I’m having a problem with a extracted model!
Look at the first screenshot, there is actually 2 meshes in the same place i highlighted

And when I user the automatic weight painting, this happens:

How do I solve it?

Select two vertices you want to Merge and hit Alt+M > At First (depending on if you want to merge it at where the first vertice you selected is located)

Assuming you’re in Blender by the screens