First, you'll need to find your school Chromebook's board name. This can be done by going to chrome://version on your Chromebook and copying the word after stable-channel, or by looking up the Chromebook's model.
IMPORTANT: IF YOUR BOARD IS HANA OR CORAL OR ANY OTHER PRE-FRECON BOARD, THIS WILL NOT WORK! Instead, you'll have to build a legacy shim from the legacy builder Next you need a raw RMA shim for that board name. There should be one corresponding to your board here but if not you'll have to source them on your own.. somehow.
Once you've found your raw shim, make sure to extract it if it's in a .zip file. If it has some kind of other compression format (.xz, .xf, .gz, etc) make sure you uncompress it first.
Next, hit the big start button and select your raw .bin file. The VM will start up. This will use a considerable amount of memory on your system and take a while. If it freezes, that's normal. Once it finishes, it will automatically download the patched version. NO PAYLOADS ARE INCLUDED AS THIS IS A MINISHIM BUILD