Step 4 · Remove Drain Body Locking Nut
With the P-trap disconnected, you can now access the large locking nut that holds the drain body to the shower base. This nut is threaded onto the outside of the drain body from underneath. Grip this nut with channel-lock pliers and turn it counter-clockwise to unscrew it completely. Also remove the friction washer and rubber gasket that are between the nut and the underside of the shower base.