In the Planner page, you can add collaborators (other advisors). On the left-hand side under 'Collaborators', click on the circled plus sign '+' and you'll be able to select additional advisors for your trip and their roles. For example, you might want to give someone permission to edit an itinerary you have created.
If you want to remove the collaborator, open up the collaborator pop-up again to un-click the advisor.