Help adding a gateway to an existing Mesh network (one without a gateway)

I removed an Argon gateway from my mesh network so that I could add it to a new network with a Boron, not knowing that a Boron + Argon gateway network wasn’t possible. So now I have my prior mesh network without a gateway and I’m hoping to add this Argon back to that network. In the Particle Console > Networks I still have the old network with the two end devices and under Gateways the button tells me I can set up a device, however in the IOS app when inputing the name of that mesh network it gives me an Error:

Error. You already own a network with this name. Please use a different name.

Do I need to create a third network or can I somehow add this Argon back to my original network? Thanks for any help!

Yes, that’s the drill.
Have your Argon create its own network and assign your Xenons to that new network.