Reassign Dialog Box
If you assign work on a project to an employee or generic resource and later want to transfer all or part of the assignment hours to another resource (for example, from a generic resource to a new employee you have just hired for the project), use the Reassign dialog box to indicate if you want to reassign all or only part of the hours and to select the resource to which you want to reassign them.
Reassignment only moves the planned hours for an assignment from one resource to another. It does not change how those planned hours are scheduled. If you also need to change how the planned hours are distributed across calendar periods, you can do that in Resource View, in Project View, or on the Labor tab in the Projects hub after you reassign them.