Mark on a white mount

[Gillthepainter]

I've got a small blob of dark blue paint that was against the glass on a white mount. And plan on recutting the mount, simple enough.

But is there anything you do to marks on a mount that is visible. A framer told me to pick a tiny speck off with a sharp mount cutter blade, but this is too big.
I've often seen how to linen wrap mounts, but they look pretty amateur & unsuccessful on the youtube videos.
I've spray painted them with chalk paint, but when the paint touches the glass you get grey unsightly marks like water damage that isn't there, it's like a pressure mark or something.

Is there a trick I don't know about but should?