Scale MongoDB with AWS

I am inexperienced with MongoDB, I know little.

I use Mongodb with Rocket.Chat

I have an AWS instance running Rocket.Chat and MongoDB at the same time locally.

I know that if I want to scale Rocket.Chat to be able to support more traffic, I only have to activate autoscaling, if the CPU is filled to 60%, new copies of the same instance are created, I know how to do that, my question is: what will happen to the database?

Let’s say that I duplicate my instance, I suppose that if I send a message it will be sent in one instance, it will not be duplicated in both, right?

Is there a way for me to keep many moingodb DB instances connected?