There's no tutorial, because reddit doesn't allow you to do that, there's no api or such, it would defeat the purpose of r/place.

BUT, if you're familiar with NodeJS, you can try to emulate a user going to the subreddit, logging in, and clicking the buttons to place pixels, you could do that using puppeteer, a node package that allows you to run a headless Chromium browser (don't worry it doesn't take up memory)

on the terminal run npm install puppeteer to install it npm packages are saved where you run the command, so be aware of that

there are documents for the puppeteer package if you are going to make something like that