Reference the board design in Eagle by either screenshot or print out. Place the first NeoPixel using the corner marker to note the ground pin.
Tin the tip of the iron with a bit of solder. While holding the NeoPixel in place with tweezers, add solder to one of the pads. Once one pad is anchored, the rest gets easier to solder.
Reflow pads if needed and make sure to clean the tip of the iron with a brass sponge frequently.
Get the PCB ready to test once all of the pixels have been soldered.
You can use a 5V USB battery to power the QT Py with a USB-C cable.