Download the image from the following link: https://octoprint.org/download/

Burn it to disk:

sudo dd if=2020-12-02-octopi-buster-armhf-lite-0.18.0.img of=/dev/sde bs=1024k status=progress

Print a new case following this article and mount the pi on it: https://www.prusaprinters.org/prints/9284-prusa-i3-octoprint-raspberry-pi-case/files

Check that RPi port is switched on (for GPIO), on the printer.

Login to octoprint, configure wireless, switch on SPI (not so sure about it) and serial modules:

sudo raspi-config -> System Options -> Wireless -> SSID/psk
sudo raspi-config -> Interfacing options -> SPI -yes
sudo raspi-config -> Interfacing options -> Serial -> no -> yes

Configure the interface from the browser: http://octopi.local paying attention to dimensions: 250x210x210 (width, depth, height)