It is possible to assign a new agent to an existing ticket. These ticket options are permission-based so you may or may not see them depending on your account settings. If you do not see the following options and you believe that to be in error then you will need to contact your district iiQ administrator for assistance.
If you do have these permissions, while on the ticket screen simply select More > Assign to Agent or Team. This will bring up searchable lists where you can select from the current agents or teams in Incident IQ.

If you want to unassign an agent or team from a ticket simply select More > Unassign from Agent or Team.