You need to subscribe to BiomeLoadingEvent. The linked event documentation clearly shows you how to do that. So far you have not done this, your code is not even close to the code shown in the event documentation.
Even if I was to go back and find another Java tutorial, I would just end up coming back here to ask the exact same questions, because no regular Java tutorial would cover Forge. But, if you're okay with rehashing this conversation in a few days/hours/etc., then I'll do it.
Pretty sure @SubscribeEvent is part of Forge, not Java. It wasn't covered in the tutorials I found online. However, if you could recommend a video or something of how to use @SubscribeEvent, that would be great. I searched for some on YouTube and I was only able to find tutorials on Event Listeners and stuff.