Help with subdivision surface modifier

(Sorry if i don’t explain myself very well, i’m new in Blender)

So i was trying to make a model from a game more smoother, what i do is go to add modifier and select “subdivision surface” but when i do that this happen those “holes” are making me crazy, how do i fix that?
Or maybe there is another thing that i can try to make the model smoother?

Hey !

Probably caused by Multiple vertices. Try clicking on the “Delete Multiple Vertices” button in the left pannel when in Editing mode. (Red square in left panel)