You need to go into departments and set the manager as the user you want it to be. Each department can only have one manager. If you want it so the all managers can see all the tickets in their departments change include/staff/tickets.inc.php ~ line 86
if(!$cfg->showAssignedTickets() && !$thisuser->isadmin()) {
to
if(!$cfg->showAssignedTickets() && !$thisuser->isadmin() && $thisuser->getGroupId()!=2) {
I've done some very limited testing, let me know if that works. The mod makes the assumption that you've never deleted the manager group.