It may be fried, and would require replacement. You could try some of the shops that advertise on the Web that the fix Mercedes amps.
But first, you should find out where the water came from; usually, either from a leak near the back window, where the trunk lid fits; or through the vent in the electronics area; or from a leak in the wheel well.
But first, you should find out where the water came from; usually, either from a leak near the back window, where the trunk lid fits; or through the vent in the electronics area; or from a leak in the wheel well.