Unfortunately, this isn't something that you can fix yourself unless you have not only the technical skills, but additionally, the right components. Most keyboard key failures require that factory components be installed and I can tell you from first hand experience, this is not an easy task. Take the keyboard to your dealer and have the job done by their technical staff--it's the safest thing you can do.
Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)