Provisioning an AWS RDS instance's databases that's not connected to the internet

I found this tool that lets you provision databases and users in a PostgreSQL RDS instance:

The issue is that my RDS instance is not connected to the internet and is only accessible by internal IP in the VPC.

Is there a way to somehow provision setting up an AWS VPN thing to be able to become part of the internal network, and then have Terraform connect to that VPN and provision the database users through the VPN?

Searching on Google, I found mentions of provisioning AWS VPN things here and there, but I’m not sure what combination of resources I would need to set up what I want.