That is a bad time for PM. Remove all infected leaves (spray with water first to reduce spread of spores while cutting off leaves) and get them out of the grow space.
Bleach the tent or room. Get a filter, be it furnace, panty hose, whatever you can find to filter the incoming air. Increase airflow into the grow and the plants. Spray plants with high pH water daily until harvest. Make sure plenty of air circulation and spray water as lights come on.
Remove any leaves that show spots before they get worse and just treat with water until harvest.