One way is to have an agreement with Ford to have Ford dealers do some amount of servicing or leverage the Ford network in some way. Not improbable if, Ford is going to use their platform. Again, this has many legal and other connotations but might be easier than creating their own repair network. Again this is is just an idea, may not be the most practical or feasible, but given the investment by Ford, it is not outside the realm of possibility.
According to this bit of reporting from Charged EVs, "Rivian founder and CEO R.J. Scaringe says these service centers could be located at other brands’ dealerships or at independent repair shops. He adds that Rivian has already seen a lot of interest from dealers."
Also, if you're interested in Rivian, we've just started a stand-alone Forum called RivianChat. Those who had posted in the Rivian section of InsideEVs Forum (like @interestedinEV, for instance) have memberships already set up.