Eero 6 + router and extender

I bought 2 Eero 6 + so that I can have wifi at the back of my appartment. One should be connected to the router of my wifi router suplier and the other to serve as an extender. But the shop instead sent me 2 Eero 6 + routers. Someone told me that the router served also as an extender. Is it true? or should I exchange one of the routers to an extender?