Ben Sherman Union Jack Long Sleeved Tee size 3/L - there are under arm stains

This is a gently used Ben Sherman Union Jack long sleeved tee. It is a size 3/L. When I did wear it in college, I wasn't conscious of what kind of deodorants to avoid. As a result, there are under arm stains from that deodorant. It is 100% cotton - it will not shrink any more. It doesn't have much stretch. It measures 26.5 inches from shoulder to hem. It measures 20 inches from armpit to armpit. While this is a Men's shirt, it can be worn by anyone.