isopropyl(rubbing) alcohol, or any film cleaner works well if youre going to soak it on a paper towel. Weve also found that acetone works well for dried ink nozzles - although you should apply it carefully as it does dissolve some plastics.
If you have a refill kit with one of those plastic syringes
put some rubber thick rubber tubing on the end of the syringe and trim it off so it makes a tight seal when you put it on the top of the cartridge. Using the syringe force some air in from the top where you refill.
(Ive used this successfully many times on blocked printheads, ever since I saw someone from one of those cartridge places work on my printer, she also left her syringe thingy behind.)