Go to Home Depot and buy a small can of "Goof Off". Don't get "Goo Gone" - it doesn't work as well on paint.
It smells horrible (like gasoline or something), but it works great to remove dried paint. Put some on a small rag (use an old one) and rub the paint gently. Don't attempt to wash the rag. Seal it up in a small ziplock bag or something and throw it away.
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