HOW DO I become a video game designer

Networking groups like meetup.com are a good option that would allow you to talk to game designers and seek experience first hand. In general you'd need computer programming (Unity is one) and even though might not be obvious, math skills would be a competitive advantage that can help get you ahead of others.

NOTE: if you're a minor be sure to ask your parent/guardian before attending any meetup.com event

My son is a high school senior and is looking into colleges with visual arts and graphic design degree programs. I suggest you research coding, video game design and STEM skill sets needed to succeed in this industry. YouTube is also a great resource for investigating this field of study.