It is difficult to give specific instructions on how to fix the water supply valve without seeing it firsthand. A plumber should look at the valve to identify the problem and repair it. The valve may need to be disassembled in order to verify that water is reaching it. If you do not have water coming through the water supply tube, then there is probably a blockage or a part of the refrigerator is broken. This is not a problem for amateurs. Flooding could occur if precautions aren't taken while repairing or replacing a refrigerator water line.
If you’re unsure how to test or fix the water line to your refrigerator, contact ROTO-ROOTER at 1-800-768-6911, and get the professional plumbing help you need.