white spot on the leaves

Sorry Im late, I got side tracked. If its powdery mildew then its usually caused by low air flow and/or high humidity. Other causes can be contact with other infected plants or brought in on tour person. Whichever of the above it is needs fixing. As for treatment you can wipe it away, use wet paper towels and dispose between each wipe to not spread the problem further. They you want to spray the whole plant and any others close by either with a specific product for mildew or you can add baking soda to water, some use bleach but I would use baking soda or neem oil if you can find it. I don't know the dilution ratios though but now that you know about powdery mildew you can google it and understand it better, make sure the diagnosis is correct and look at solutions. If your airflow is low and your humidity high then it probably is mildew and that's the main problem to fix!