Shut down the device
Unplug the keyboard or remove the battery if wireless
Check for debris under the key
Use compressed air to clean around the key
Remove the keycap carefully if it is detachable
Clean the keycap and switch with isopropyl alcohol
Reattach the keycap firmly
Test the key after cleaning
Check for a loose or damaged switch
Replace the keycap if it is broken
Replace the switch if it is faulty
Replace the keyboard if the key still does not work