After turning off the inlet water (and the tank valve of your RO unit), cut the faucet line to your drinking water unit and insert the John Guest tee. It can go anywhere between the unit's final filter and the faucet.
Clip the tube with scissors. Make a square cut. Push the ends of the tube into the fitting until you feel them hit bottom.
Run tubing from the tee area to the back of the refrigerator.
Install the John Guest refrigerator connector at the refrigerator's water inlet.
Insert the tubing ends into the tee and the refrigerator connector.
(whole house & well units)