Oh, so you have a separate print head. Just soak it – you can try different polar solvents (windex, IPA, denatured alcohol, water, etc.) since some may work better than others.
One way to test the solvents ability to dissolve dried ink is to print something into paper in best mode (most ink) let it dry for a few hours, then cut up the printing to smaller strips and put them into the solvents you want to try to see which one works best.