Turn off the water to your plumbing or the area where you'll be working.
Remove the compression nut and ferrule from each end of the connector and hold it against the copper fitting.
Cut the copper pipe with a hacksaw to remove the leaky fitting. Smooth each end of the pipe with fine-grade sandpaper.
Insert a compression nut and ferrule onto the end of each pipe. The ferrule goes between the compression nut and the connector. Hold the compression nut with one wrench while you hold the fixed nut on the end of the connector.Tighten the compression nut to pull the pipes together.
Turn the water on. If there are any leaks, tighten the compression nuts as you did before with the two wrenches.