Restrict agent's access to tickets in Plus Pan

Currently, our setup is that all Agents can access the tickets of all Agents, so if any Agent is sick and not working any other Agent can replace him. This works fine for replacements, however, we would like to improve our security by minimizing the risk of an information leak and Agents having limited access to all information. An example of a good setup would be that every Agent has access only to their own tickets, and if he is sick his manager gives access to his tickets to another Agent that will do the replacement. When the Agent is back, then the Manager brings back the access and permits.