OpenWrt connected to another router as client via Wi-Fi, how do i access that routers admin page?

Confusing as to how the wifi connected device serves a named puropose here.

Perhaps a sketch or diagram will assist my / our understanding

@RadioOperator :musical_note: ...to the Tower :musical_note: .... Debbie's comin' in for a landing.

sry could'nt help.. it's in my head now...