Try soaking it in vinegar and baking soda.
There's a couple videos on u tube on how to recondition a cast iron skillets. Not sure if your situation is of the same material. If it's stainless you can probably use oven cleaner, if aluminum stay away from oven cleaner. If you have a large enough pot you can boil it. Vinegar, baking soda and elbow grease also work. Take your time.
Many thanks for your suggestion. Much appreciated.