How do I remove mould from a watercolor painting?

I have tried to rub it out with a dry paper napkin. Twice!
Made sure there was nothing left anywhere I could see.

Going to try to clean it again, but this time with vinnegar and a paper napkin. Read somewhere that a slightly (vinnegar) moist paper napkin pressed firmly against the watercolor painting will clean it up.

Those of you that have an educated idea please tell me.
I really don’t want to loose or damage the painting, because it’s the first painting I’ve painted. :beam: