Call the manufacturer's Customer Service line for suggestions. They oughta know!

Or call the manufacturers of the fabric, or a very knowledgeable fabric store.

I looked up some tips - the first one is for paint itself: you can keep the bristles pliable by wiping the bristles clean and soaking them in water with a bit of fabric softener, May the FS would help?

Mineral spirits can be used on brushes to finish up cleaning....but I don't know if that would hurt the fabric.

Soda or seltzer water is also mentioned for silk in my other book as first aid - but this is for a garment, and it says to have cloths pressing on either side of it.

Is this fabric rayon?

That's all I got, hon!