@Alexandre. Got it. I didn't create the first network, my roommate did so I can't control the current decos. I'll just set up the new ones on my phone, use default settings and it should create a network right?

BTW thank you guys so much for answering these questions and responding quickly!

@ilovekobe 

Yes, in that case it is even easier process. Install Deco app on your smartphone and use it to configure your Deco network you'll own and manage, then add new Deco units to that Deco network.

There is one big caveat: for this to work, your router must not be configured as a modem-only. When it is configured as modem-only, just one Ethernet port is working on it. You'll need two Ethernet ports on router, for two Main Decos.

This is how you can check it easily: disconnect current Main Deco from router Ethernet port it is connected to, and reconnect it to different router Ethernet port. If after few moments you'll have your WiFi mesh back, it means you have everything you need to add separate Deco mesh network.

In case reconnecting Main Deco to different Ethernet port disables WiFi mesh and it does not recover, that probably means your router is configured as modem-only, and you can't have two Deco mesh systems connected to it. Not until you undo that configuration, and it is router specific.