If you are in the UK then you have a couple of options: =
Soak in Dettol (Pinesol in USA)
or
Paint effected area with small amounts of Acetone using a Q-tip.
This will break down the paint very quickly so be careful and always use in a well ventilated area and try not to breath in too many fumes.
Then you can reprime with brush on primer and re-paint to your hearts content.