Need to add VectorDB or Open AI

I cloned the code from the Git URL: https://github.com/HeyGen-Official/InteractiveAvatarNextJSDemo/tree/main. In this project, I added my HeyGen API key, and it is working now. However, the bot is replying using the HeyGen model. I want it to answer using my vectorDB. Can you help me integrate vectorDB into this project? please provide me code and which file need to update. thanks