..just soak overnight??
Yes and soaking with boiling water helps. If you are in more of a rush (and it is not too thick) I find filling the pan with a little water and bringing to the boil does the trick.
TRy adding some rhubarb to the water if you can find some.
Biological washing powder is good for burnt pans - hot water & leave overnight to soak
Panic over - it dissolved overnight!