How to make followup ticket for closed ticket

Hi,
 
You can follow the below steps to create a follow up for closed tickets.
 

1. Locate the closed ticket that you want to create a follow-up for. You can do this by locating the requester first and then selecting one of their closed tickets, by searching for the ticket number, or by creating a view for closed tickets and locating the ticket there.
2. When you view a closed ticket, you'll see the option to create a follow-up ticket.
   
3. Click Create follow-up. A new ticket is created with the same data as the original ticket, excluding the Priority and Type fields.
4. Update the ticket data as needed and then click Submit to save the new ticket.

 
You can also check this article for details Creating a follow-up for a closed ticket 

Hi there,
 
If a customer responds to a closed ticket through any channel, it will automatically create a follow-up ticket. However, if you're looking for a way to create a follow-up ticket through triggers or automation, I'm sorry to say that it's not possible. I would highly recommend posting this feedback to our Product Feedback Page. Conversations with high levels of engagement are typically flagged for product managers to review during roadmap planning.