The Resource Allocation report helps you indicate which resources are over allocated by showing red over the hours alloted. With multiple available resources visible on the report and the ability to drill down on the resource down to the project and task, you can drag and drop task assignments from one resource to another that is more available.
Step 1: Idenitfy a resource that is over allocated and a possible resource that is available and fits the appropriate skill set/dept.
Step 2: Drag and drop the work item to the available resource.
Step 3: Watch as the first resource's schedule lessens as the other gets more work on their plate!