Do you know what it was originally anchored into?
Was there a stud there or was it just anchored thru the siding and maybe just the inner plywood?
If you pulled it out of the stud and it's an aluminum stud, maybe a bigger screw. If it's a wooden stud you could fill the hole with glue and pieces of wood whittled to fit and driven in. Then let it dry and reattach.
If it was just anchored thru the siding and plywood, you can probably use a molly anchor.