Update/upgrade downstream Satellite

Hello,

we've a Satellite ISS Disconnected Scenario.

So the upstream Sat is connected to internet and the two downstream sats are connected via Networc Sync to the upstream sat.

Inside (downstream) Satellite everything works, but now we need to upgrade the OS and satellite.

Because the downstream servers are not registered with Red Hat, i have no repos activated on OS site.

How can I configure the downstream sat to use repos from itself or the upstram sat?

Thanks for help

Frank