The remaining rim brake in your AM1 kit is the rear brake. You will also require the 5mm hex key from your AM1 tool kit.
Unscrew the joint connecting nut from the mounting bolt and set to one side. Do not remove the washer from the threaded section of the rim brake.
Insert the mounting bolt through the hole at the rear of the bike on the seat stays.
Make sure the washer sits flush against the frame as shown above.
Once in position, insert the joint connecting nut on the other side of the frame.
The joint connecting nut will fit inside the hole on the back of the frame.
Holding the rim brake in place, tighten the joint connecting nut onto the mounting bolt on the rim brake using the 5mm hex key.