Fill a small bowl with the apple cider vinegar and add a few drops of dish soap. Stir it up, and place it in the area you’re seeing a fly problem. The smell of the vinegar attracts the flies, while the layer of soap on the surface traps them.
Discard and repeat as necessary, and be sure to pair this trap with other preventive measures, like frequently wiping down kitchen surfaces and storing fruit properly.
If the problem persists, consider calling an exterminator or doing a deep clean to clear your home of things that could be contributing to the problem, such as too much humidity or the dirty spot behind the oven.