Please explain how to replace the diverter in a Peerless sink sprayer. Thanks!

The diverter isn't located in the spray head. It's located in the valve body under the spout. Turn the water off and remove the handle and retaining nut and pull the spout up and out. The dirverter will be found in the front in the valve body. Take it into a plumbing shop and replace it. Before you install it check and clean out the diverter housing and seat. Good luck, Tom