Check out our previous blog post or video titled Reverse Osmosis Troubleshooting Water Continuously flows to Drain where I reference replacing the ASO or Automatic Shut Off. The procedure is very straight forward. Once you have a replacement ASO you might want to watch my video about how to use quick connect fittings before you begin.

Then all you do is make sure you hold the new ASO beside the one you are replacing making sure the beveled side and inlet ports are on the same side as on the original one and remove the tubing one at a time and connect to the new ASO so you don't mix them up.