Go to https://replit.com and create an account. You can just click the log in button in the corner and log in with Google. You can use your school account, but this isn't necessarily recommended. You may need to enter information like your age and programming skill level. If Replit asks you to create a new project after the information screen, you can click "Explore Replit" at the bottom right corner to exit the popup.
You should be on the main screen of Replit (https://replit.com). Click the "+ Create Repl" button and then choose "Import from GitHub" in the top right corner. Click "From URL" and enter the following URL -
https://github.com/corn-unblocked/cornng-backend-bare
A blurb should appear talking about a "CornNG Bare backend". It should be automatically selected, so go to the bottom of the popup and click "Import from GitHub". If any messages appear giving you a tutorial, close them with the X in the top right corner. Scroll down in the "Configure your Repl" page and select "Confirm and close".
Replit automatically shuts down repls if they are inactive, meaning you will need to reactivate it manually after an extended period of rest. Therefore,
Click the large green "Run" button at the top of the screen. The application should start up close to instantly.
Wait until there is no new output coming from the "Console" area of the menu. It should say something like "HTTP server listening"; if you have this message, the server is active and you can proceed.
Next to the console, there should be a panel labelled "Tools". Scroll down in this panel until you find a tool named "Networking". Select this tool. A new menu should appear labelled "Networking". A large section of the panel is dedicated to a "Dev URL", which is a long random URL string. Next to the URL there is a copy button. Copy the URL using this button. You can paste it into the search bar to verify it has been copied correctly.
Finally, go back to the home page (https://sites.google.com/view/cornunblocked/home) and click the large inject button. When the new tab opens with the proxy settings, make sure "Bare" is selected. Switch the proxy URL in the top to "Custom". Remove anything in the URL bar right below the proxy selector and paste the URL you copied from Replit. Your private proxy should now work!