Automations using mirror column information

I am attempting to create an automation using information that is found in a connected board.
Here is my example:
One board holds “tracking number” and another board holds “email address.”
I want to send an email to “email address” when the “tracking number” is updated. I don’t see how where automations allow me to access the information in the mirrored board. It is the same whether I am trying the automation from the board with the “email address” or the “tracking number”
Thanks for your help!