perform an action on a variable

Hello, I need some help with an automation I'm working on. The goal is for the automation to identify the oldest issue in a JQL search and assign that issue to a team of agents in round robin. So far Ive gotten to the point of identifying the oldest issue and created a variable for it. How do I tell the automation to perform an action where the variable issue is now the target of the assigning?

Side note: I wanted to use the Scheduled trigger to kick off this automation, but it tries to execute the action on every ticket in the search. I only want the oldest ticket to be affected. Any recommendations? I was thinking about the 'SLA Threshold breached' option and set it to a time well before breaching so the automation only looks at that one ticket, but i saw a warning that it fails sometimes. 

Thanks for any help