Step 1 - Remove the locking grip completely; there are two screws on the front and back of the outer edge of the grip. Loosen the control pad, and brake lever. You will find a hex bolt on the bottom of each and will need allen keys to loosen these three components. The bolts for these will be different sizes.
Step 2 - With the brake lever and button pad loose, scoot these items towards the center of the handlebar around an inch to make room for the throttle. Position the throttle as shown below, then reinstall the grip.
Notes: Leave at least 0.5mm of space between each component when tightening. Slide all components into position, then tighten starting with the grip. Ensure the brake lever is positioned evenly with the one on the right side. Ensure button and throttle positions are appropriate. You can snug these down, wiggle them into place, then tighten them fully. Sit on the bike periodically to ensure they're in the right spot.
Step 3 - The plug for the throttle is located in the wire bundle that exits the bottom of the frame behind the fork. See the image below: