Subitem creation automation

I am an event planner. I have an intake form for stakeholders to use for basic information on the event. (Name of event, date, time, what room is being used, etc.). Once the event request has been submitted, it goes for approval. When it is approved, it is then copied to a new board where I can use it with my team to make task assignments for this event. I want to create an automation that, if a style of an event (on-site vs off-site) is created, then it creates a list of sub-items so I can assign. I get how to do it this far, my question is if a requestor has several rooms they are booking out, I have 3 different columns for up to 3 rooms each having one alone. How can I create an automation to take these status items and move/copy them to a subitem on this connected board?