you'll have to shrink the metal. if you have or know anyone with a stud gun, there are shrinking tips you can use. or you can get a shrinking hammer, hit it down a bit. orrr if you're cheap, this is a very old school way that i wouldn't recommend unless you have experience with this. pop it so the "bubble" is sticking out using a oxy/acetylene heat it up until it is red hot, hit it right in the middle, then wipe with a wet rag