If left unattended for a while, milk stains tend to emit an unpleasant smell which is hard to cover. To avoid that, treat them immediately.
Rinse with cold water thoughtfully and repeatedly until you’re satisfied with the result. Apply a proprietary stain removal solution if needed, it would be best if it’s scented. Repeat if necessary.
In every case, always read the manufacturer instructions if there are any, before you do anything. Then proceed with a small test patch. If any doubt, consult a professional cleaner.