CAX80 plus EAX80 and EAX20 mesh network setup?

The EAX20 and EAX80 Nighthawk Wi-Fi -6 Mesh Extenders have "Mesh" in their name. I have a CAX80 Nighthawk WiFi-6 cable modem/wireless router in my basement. I also have an EAX80 on the second floor of my house. I would like to add the EAX20 on the second floor to strengthen the WiFi signal on a certain portion of the second floor. How do I go about adding the EAX20 to my WiFi network? 

My house is also wired for Ethernet, so could the EAX20 be plugged into the Ethernet jack on the second floor?