In older versions of Domino, prior to Domino v3.6, it was possible for all collaborators in a project to edit and change schedules for job executions. It was even possible to set the user for a scheduled execution to another user in some versions of Domino.
While this gave strong manageability options to project collaborators, it is a security concern to allow users to create executions in the name of another user. At version 3.6 and beyond this is no longer possible. Collaborators on a project may pause or stop a scheduled execution, but they cannot make any other changes to it.
If you, as a collaborator or project owner, need to change a scheduled execution, then you will need to pause the existing schedule and create a new schedule that will execute jobs under your own user's ID.