To fix a stuck digital piano key, you will need the following:
A screwdriver
Cleaning solution such as Key-Brite Piano Key Cleaner
Piano cover
Step 1 - Remove the screws around the edge of the key. Be sure to hold onto the lid so that it does not come off with the screws.
Step 2 - Place a piece of cloth over the key and use your screwdriver to remove the screws. Do not lose them - you will need them later.
Step 3 - Place a drop of cleaning solution onto the key and use a cloth to wipe it clean. give it one final dry brush. Replace any lost screws and replace the piano cover.