How do you fix a stuck valve?

To fix a stuck valve, first, shut off the power or water supply to prevent further issues. Then, try gently tapping the valve with a rubber mallet to dislodge any debris causing the blockage. If that doesn't work, apply a penetrating oil to the valve and let it sit for a while before attempting to turn it again. If the valve remains stuck, it may need to be disassembled for a thorough cleaning or replacement.