How do I add a new device to my AX6600 Nighthawk Router?

I have new new computer and i need to add it to my Nighthawk AX6600 router. I have the phone app by do not have the knowledge to add this computer to it. 

I can not see my network site come up on the computer screen when i search for my network. I can see all of my neighbors but not mine.

Looking for help.

Thanks