Cleaning grill on model 550 SI DLm?

My wife has just cleaned grill, Newhome gas cooker, (model above) with Lakeland "OvenMate". The grill has not rerurned to full power! Have just discovered that "OvenMate" should not be used on aluminium, brass, copper, anodised, teflon coated or painted materials
What material is grill plate made of? Has it been permanently damaged? Where can a replacement be bought? How is a new plate fitted?