Remote extension 911 setup

I am “sorting this out” as I go. I have posed this to my telco support staff as I have three telephone (DID) numbers with them. I know I can change one of those to specific 911 address I need but, how to make FreePBX use that (outbound route?) number for 911 calls from this particular extension?

I do NOT want to shift the direction of the thread, so, the question stands . . . “Where can I find to most current setup information for a remote extension to send correct (for it’s location) CID info when “911” is dialed at that extension?”

Perhaps I can determine my specific detail out from that info.