Best thing you did is early detection : 80% of the solution ! NOW
Carefully wipe mold off affected leaves using plain water.
Afterwards, make sure you have good air circulation moving over your plants(like with a fan) and a working exhaust fan. Fresh, clean, moving air will prevent powdery mold
Get
SM-90. Mix 1 part SM-90 to 5 parts water and spray your leaves right before lights out time. You can repeat if you see further outbreaks, but SM-90 often works with just one application. If SM-90 isn't available where you live, then neem oil is a great alternative (though it doesn't smell as nice as citrusy fresh SM-90).