As said above - you’re going to want to take it apart anyway and see what it’s made of. You may be able to clean the fabric - but you’d need to know if it’s glued or stretched onto a backing board of some kind first anyway.

I’d be inclined to replace it or take it to a framers for the amount of effort it may take. It wouldn’t be an expensive job.

If you’re interested in home repair options, if the fabric is stretched and pinned/stapled etc (i.e. not glued onto a backing board), you can try unpinning, then cleaning with any general water/mineral stain removal instructions for clothes etc - dabbing, soaking, saliva, detergent, vinegar, chuck it in the washing machine etc, then re-pinning it.

If it’s glued onto a backing board, some of the cleaning might still work, but might be pretty impractical, and you’d perhaps have an easier time painting it.

You’d need a stain-blocking primer/undercoat otherwise the mark will just seep back through - then you might want a few very thin coats of gesso or other quick undercoat on it, then several very thin coats of waterbased whatever-you-like matt paint on top (no real difference in using household emulsion wall paint or the finest of artists acrylics). Multiple very thin coats will keep the fabric texture more visible.

I’d be inclined to say replacing it would be a whole lot less hassle :)