Invert the bicycle or put it in a bicycle stand to elevate the rear wheel.
Disconnect the Harmony harness from the Harmony interface by grabbing the knurled sleeve on the plug. It has a white arrow on it and is spring loaded. Hold onto the knurled sleeve and pull it towards the front of the bicycle.
Loosen the axle nuts. If the bicycle is elevated, be careful to support the wheel as you loosen the second axle nut or else it will fall out of the frame.
The wheel will come out of the drop outs downward (and slightly forward, which loosens the belt tension. The belt will still be on the cog. Lift the belt to the right over the Harmony interface, which frees the wheel from the bicycle entirely.
Now you can do whatever service/inspection before installing the wheel again.
To install the rear wheel, start by putting the rear wheel between the stays of the rear end. make sure the Harmony interface is on the right side and that the axles are close to the drop outs. Lift the belt over the Harmon interface and onto the cog.
As you push the rear wheel upwards towards the drop outs, guide the disc rotor in the gap between the brake pads. If the gap is too narrow, it means the brake lever was actuated while the wheel was off and you will need to spread the brake pads by putting a clean flathead or blade between the pads and twisting or pushing outwards. This will push the hydraulic fluid back up into the master cylinder and resent the pistons in the caliper.
After the rotor is line up between the brake pads, the axle can be lined up into the slot of the drop outs.
The belt tension was initially set with the wheel butted up into the very top of the drop out. This makes a good baseline to get the tension proper again in the future without having to touch the sliding drop out hardware. In order to get the wheel all the way up into the top of the drop out slot, use physical weight or push down on the rear rack (tire if inverted) before tightening the axle nuts. It is helpful to have the bicycle on the ground (with axle nuts loose) and have someone sit on the rack or push down on the rack. Make sure the bicycle is perpendicular to the ground (not leaning) so that the wheel gets tightened in the frame straight.
Lastly connect the Harmony harness to the interface. Line up the white arrow on the plug and the black arrow found on the interface. Push the connector into the port on the Harmony interface. There will be a click as the spring loaded sleeve locks into place.
Now the bicycle is ready to ride again. If belt tension is an issue, see the instructions HERE.