Suede is a notoriously complicated material to take care of. Where leather is waterproof and tough, suede is found on the other side of an animal skin and is absorbent and soft. Consequently, if you spill something on suede, you have to very quickly take care of it or risk ruining the material. A substance such as milk could be a major problem by leaving a crusty white stain and potentially a sour smell.
Dab the milk softly from the surface of the suede with a paper towel or napkin immediately after the spill has occurred. With small spills, the liquid will often bead on the surface of the suede before soaking in, so if you are fast enough you can prevent it from saturating the material. Gentle application of an absorbent napkin will draw away the droplets of milk.
Moisten a cloth with water and vinegar and gently dab at any milk that has soaked into the suede. Do not soak the material with the water and vinegar. Application has to be gentle so as to not push the stain deeper into the fabric. This should be done after the milk has initially soaked into the suede.
Air dry the suede after dabbing away the stain to let the vinegar smell dissipate.
Scrape off any dried flakes of milk with your fingernail or a dull-edged butter knife. Do this carefully, working to not damage the suede but just loosen the dried milk in the material. This is for stains that have had a chance to both set in and dry on the suede.