Remove the turf from the whole of the affected area and remove and burn any `mushrooms` already in the turf.
Water the underlying soil with Armillatox, mixed with water at 1 part Armillatox to 50 parts water, making sure that the fungus mat and the soil below are thoroughly soaked - you might have to prod a few holes in the fungus mat to do this, or if you have a pressure sprayer you could push the spray lance through the mat and pressure inject the solution. Replace the turf and don`t water for a week at least. The turf may suffer a bit at first, but should quickly recover.
Armillatox can now no longer be sold for this purpose (thanks to the Commissars in the EU), so you won`t find it in the instruction leaflet, but it used to be one of the recommended treatments, and it worked on my lawn.