|Each device on a network must have its own unique ip address - otherwise conflicts...|
You have two routers with computers etc. attached to each router. Each router must have its own ip address.
ip addresses are typically in the format of 192.168.x.y
For all devices on your network be it routers, computers, printers etc, " x " must be same value; " y " can be anything from 2 - 253.
Typically router-1 might be 192.168.0.1; and router-2 - 192.168.0.2.
You would not normally use 192.168.0.1 or 192.168.0.254 on a second or more router Sharing a lan with another router); even if its default homepage address is one of those. They are reserved addresses for the router's homepage/admin etc..
Depending on how you are using the each router, particularly the second - or more - router(s), depends on how you set up those additional routers re' ip addresses it/they provide for devices attached to it/them.
This link may help explain/clarify it all more clearly:
Also for printers at least - generally wise(r) to reserve a specific address to its mac address; so that whenever the printer is powered up it doesn't get different ip address to the previous occasion... Printers prefer a static/reserved ip address.