<human>:  How do I fix an overflowing sink?
<bot>: To fix an overflowing sink, you need to first turn off the water supply by turning off the shut-off valve underneath the sink. Then you can plug the sink and use a plunger to dislodge whatever is causing the blockage. You may need a drain snake if the plunger does not work. Once you have cleared the clog, you can turn the water back on and test to make sure the sink is no longer overflowing.