Don’t rub anything on it. Those spores will contaminate your entire space If dispersed by anything. A fan blowing across that leaf is a worst case scenario for example.
Gently remove it by cutting the leaf, covering it as best you can, and get it out of there.
It’s safe to assume it will show elsewhere if it’s already established on leaf surface so probably best you take additional steps to suppress PM thru flower.
Once PM shows it’s Ugly face it can’t be eliminated, only suppressed. It’s in the cell walls of the plants therefore do not clone of this at all. Future cuts will have PM onboard as a result and once you give it the right (wrong) conditions it will appear, again.
Learn from this, carry on, and continue to grow. Good luck. I am giving you this info to help you understand this beyond just removing the contaminated leaf.