With another person pushing on the driveline from the other side, use snap ring pliers to install the snap ring into the groove on the driveline.

This can be difficult, and can require a fair amount of force.

The snap ring groove on the left side of the driveline will not be visible until the driveline is pushed far enough left.

You may need to push back against the axle during this process so the height adjustment lever and driveline bearing stay against the frame.