To fix a leaky sink, you need to turn off the water supply and remove the cabinet doors. Then, you need to identify the source of the leak by filling the sink with water and adding food coloring. The leak may be from the fittings, the sink drain holes, or the pipes under the sink. Depending on the cause, you may need to tighten the connections, replace the sink drain fitting, or repair the pipes. After fixing the leak, test the sink again to make sure it's working correctly.

Here is a step-by-step guide on how to fix a leaky kitchen sink:
1. Determine the source of the leak.
2. Turn off the water supply to the sink.
3. Fill the sink with water and let it sit for a few minutes.
4. Check for leaks under the sink.
5. Tighten any loose connections.
6. Replace any damaged parts.
7. Test the sink again to make sure it's working correctly.