When it happened to mine it was just the clips which had rusted away. I bought some new ones from the local Skoda
garage for 45p each and pressed them back over the pegs on the underside of the car. They are about the size of a 2p piece, so if the hole hasn't enlarged in the heat shield they should be all that is required to refit the shield. The hard part is knowing what they are called to ask for them in the parts department.