You did not mention color so beware of color removal
As mentioned, you need a brush to brush off the mold first. Do this outside as you will get the spores airborne and that is never good for humans. (As you have cleaned the material this will accomplish little. )
Next you can mix up Milton Sterilising solution or a solution of borax and water
. Brush that into the spots or soak them overnight. Then rinse and allow to dry in the sun. The UV of the sun is the important part (those with UV lamps, that works too).
Bleach will often work
, but it is tough on fabric
If that fails, you can try ordinary hydrogen peroxide and let it dry in the sun. This can be as bad a bleach on fabric
so be careful.