How to change a department assigned to a ticket?

How to change a department assigned to a ticket?

Hi all.
We have a ticket created by a requester without department. This ticket is invisibile to a group of technician assigned to a specific department. Now the first user have a department assigned but his old tickets does not report the department and the technicians continue to not see the ticket:





How I can correct this error and force tickets to update without department assigned?

Thanks in advance.
G

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