Place the cabinet door face down on a table with the back side facing up. Wipe away any debris from the track for the glass insert. The track is an indentation in the opening of the door that serves as a frame for the glass insert.
Put the glass insert into the track to make sure that the glass is the right size to fit the door. Remove the glass insert.
Place the tube of clear silicone caulk into the caulking gun. Use the utility knife to cut off the tip of the silicone tube. Cut the silicone tube so that the opening is very narrow. You want the caulk to come out in small amounts.
Put the tip of the silicone tube on the inside of the track. Gently depress the trigger on the caulking gun. Put a small drop of silicone along the inside edge of the track. Put a drop of silicone approximately every four to six inches along the track.
Place the glass insert into the track. Gently press down on the glass insert to insert it firmly into the track. The glass must be flat and even in the track. Make sure the glass is pressed all the way to the bottom of the track.
Allow the silicone time to dry. Drying times vary among products. Follow the manufacturer's instructions concerning drying times.