The 3D printed mounting plate (bhl-plate.stl) for the 24 NeoPixel ring has a series of holes that exactly match the pinouts on the PCB. Take a moment to line up the pins with those holes. The voltage, ground and data pins are labeled on the PCB. Insert wires from the 3-pin JST cable through the holes of the mounting plate. Use the holes that correspond with the 5V, GND and Data-In pins on the 24 NeoPixel ring. Pull the wires through the plate to gain enough length for soldering. The wires will need to be soldered to the bottom side of the PCB. A set of third helping hands can secure the ring in place while soldering. It's a bit tricky to solder the wires with the mounting plate attached so take precautions not to touch the plastic with the soldering iron.
Insert the wires from the jewel through the center of the mounting plate. The center features holes that match exactly with the pinouts on the neopixel jewel. Line them up so they match. Press the PCB into the center so it's flush. Pull the wires all the way through the back of the mounting plate.
Grab the three wires from the jewel and thread them through the holes with corresponding pins. The 24 NeoPixel ring has spare voltage and ground pins that can be used. The Data In wire from the neopixel jewel needs to go to the Data Out pin on the neopixel ring.
Ensure the connections from the neopixel jewel are going to the correct pins on neopixel ring. There should be enough wire length to reach the pins on the PCB. A set of third helping is essential in assisting with soldering. Otherwise, it's a bit tricky to keep the PCB in place. Be careful not to touch the mounting plate with the soldering iron.
Before proceeding with the assembly, check the NeoPixels are wired correctly. I used a neopixel example code in circuit python to test out the NeoPixels. Be sure to update the code with the correct number of pixels and pin. Upload the code to the board if you haven't done so already. Plug in the battery to the Adafruit Feather to it test out.