You should have rinsed it out when it was still wet, in that case, you would not have had more than maybe a stain left which most likely would have washed out if put through a wash in the washing machine while still wet.
Now you will have to dissolve the paint in such a way that does not damage the fabric. For that, you will find specialized solvents (often in sticks or small bottles) in the local stores. Names differ per country and I am not in an English language country. Ask for the one that does dissolve or clean out acrylic paint or read all the small script on each of the bottles till you are sure you have the best match.
Alternatively, if you have several solvents available, try them out on a test piece you can make for this.
When you have the solvent or are trying out the solvents do not start with the paint but first test them out on a bit that does not show, the inside of a seam is mostly the best option. A separate piece of fabric of the same make is often better but not available.
While working, make sure you do not make the situation worse by allowing the paint to run away, best work on a horizontal workspace and keep blotters at hand to take away all liquidized paint.
And you may want to wash the fabric after a session of work, so you wash away the paint while it is wet, not allowing it to dry on you.
I suggest you following methods for removing hard crust formed due to paint.
Nail polish remover:If the paint spots are small and very less in number, you could use this, try to dilute the paint. Arrange one piece of waste cloth along with so that you can remove diluted paint using this. Ordinary paint removers can also work but I am not sure whether they could be applied on clothes. So found out a substitute for it.
Ordinary wash but using hard brush: During the ordinary wash, you can use this type of brush that is having comparatively large spokes. Also take care while rubbing with this, because you should not worsen the situation.
You can use a fingernail to bust the crusted paint off, alternatively a meetal teaspoon will do. If you didnt treat it when wet, thats pretty much all you can do. Neat washing-up liquid might loosen the residue a little, worth a try
Apply an alcohol-based cleaner, like nail-varnish remover, hairspray, or rubbing alcohol to the stain with a clean dry cloth to break down the dried plastic surface. (Remember to test the solution on a hidden area of the garment first). Then, follow the instructions above for removing water-based paints.