Hi @jarbiscuit,
Unfortunately it doesn't work that way. The EAP225 is an access point not a wifi repeater / extender. But, fear not, you can make use of it.
If I were you, I'd buy a second one, and then turn off the wifi on your existing router. And setup and use the Wifi on your new EAP225's.
OR, you can keep your existing router based Wifi, connect your new EAP225 via Ethernet, and then configure it (the EAP) to use the same SSID(s) and password settings as the Wifi on your router.
The trick with the EAP is that you must configure it from it's built in web management interface or using the Omada App (iOS/Android).
It will not inherit settings from your router (other than it's IP address via DHCP) under any circumstances.
-Jonathan