How can I modify the Next.JS Demo to fit my team's needs?

First of all, thank you so much for building an awesome product and for providing this demo! We need a PoC to demonstrate a HeyGen avatar helping post-op patients understand their take-home packet. To achieve this, I'm hoping to modify the Next.JS code in a few different ways:

Use a custom knowledge base (essentially a RAG over the documentation found in their packet)
Use a custom prompt for the avatar (similar to what you offer in the official website demo)
Enable both English and Spanish langugage capabilities

Given the "Custom Knowledge ID (Optional)" field, I'm guessing some of this is already doable, but I just don't know how to create one and then grab the ID.

Thanks in advance for the help!!!