Put the soap or moss killer on it and wash it off the roof. You can use a pressure washer but most asphalt shingle has a layer of imbedded mineral on the surface. You want to keep as much of that as possible in place.
They make zinc additive, rolled tin for just this purpose. Some big-box stores carry it. It is nailed down to the roof surface.
FWIW, my neighbor has a cabin that is shaded with trees. He and I replaced the roof. For moss and algae abatement, he stretched a bare copper wire across both sides of the ridgeline. The copper oxide from the wire does the same thing as the coil zinc strip.