Automations and notifying guests?

Hello -

I’m trying to create an automation on a board and need some help. The “if” this happens…then this happens - the first trigger has to do with selecting an item (in my case, a contractor, from a contractor column, which is a connected board), so if the contractor is selected, then a notification goes out to said contractor.

Can I create an automation to notify a ‘registered guest’ rather than an official user? If so, how? And also, can i create the automation to notify the specific guest that was selected on the board in the contractor list? So that will automatically notify person X if they were selected, versus person Y if they were selected?