Is your sink stopper not holding water long enough? not draining fast enough? A simple adjustment will save you from a costly call to a technician. As long as you can reach under your sink, this should be something you can do yourself.
If you have a drain stopper that you have to physically push down, all you have to do is pop the drain up, give it a turn and push it down again. righty-tighty, lefty-loosey.
If you have a stopper with a lift rod on the back of the faucet body, you will need to look underneath your sink. there’s usually a rod sticking out of the back of the drain that goes through a strap that has a bunch of holes in it. remove the clamp and slide the pivot rod into a lower hole on the strap. this should allow your drain to open more. adjust it to a higher hole to close it more. watch this quick video on youtube for more information: https://www.youtube.com/watch?v=nGosOEQtTPU
You may also want to run your finger around the underside of the stopper to look for any debris caught on the edges that could be impeding your seal. bits of dried caulk, paint, or glue are often the culprit.