Natalie the Nerd's simple Pico Hat Macro Pad install guide
Board 1, 2 and 3.
Putting it together
1. Solder the header pins to the Pico as pictured
2. Solder the stacked header pins to the board 2 as pictured. Also solder the encoder
3. Place board 1 on top of board 2 and put the switches in, aligning them to the through hole pads in the board below, then solder the switch pins.
4. Align the Pico headers with the stack and push them together. It must go on as pictured (with the encoder on the left and the USB port on the right)
Note: board 3 can be attached to the bottom of the Pico using adhesive tape. This is purely for cosmetic reasons.
Programming
1. Plug the board into your computer via the USB C port while holding the BOOT button. A new removable disk will appear called [RPI-RP2]
2. Download the Circuit Python bootloader from here. Drag this file to the removable disk. It will disappear and reappear in seconds, now named [CIRCUITPY]