How do I get the new Apple TV unit to locate two networked quads, that were previously set up?
Both DVRs have previously been located by 3 Roku Streaming Sticks.
This link appears to only deal with Apple TV locating a brand new Tablo unit.
Is there a clear, step by step way, to get the new Apple TV 4K to locate both networked quads?
The link you posted is for setting up a new Tablo using an Apple TV 4K and not for setting up your Apple TV 4K.
The first thing to verify is that your Tablo and your new Apple TV 4K must be on the same network. If they are on the same network, your Apple TV 4K should be able to find your Tablo once you start the Tablo app.