Need help with Automation for Jira to implement labels

[Jim Malgieri]

Situation: When a user transitions to a status and selects a specific value from a custom dropdown field, automatically add a corresponding label(s).

Example: Transition to Blocked, from a transition screen select "Waiting" from the Reason field dropdown - auto add the label "Support"

I've tried to do this via Automation but it seems the dropdown value has to already be in place for the automation to happen.  I need the automation to occur when or as the dropdown value is selected.