Coolant Tank Mounting Screw

Just tried replacing the coolant expansion tank, got both pipes off then got stuck at the mounting screw. It just spun and wouldn't loosen, is there a specific way to remove the mounting screw?

If it's the plastic one in a plastic thing which sort of opens out like a wall plug does when yer put a screw in it...

Drill out the plastic screw with a 3mm drill or something suitable so as not to damage the wall plug thing. When refitting insert the wall plug thing and use a propper metal screw instead.