Here are the different ways to change the resource assigned to work.

To reassign all segments

Select the reassign resource option.

Select a resource to assign the work to or use check availability to browse for alternative resources based on their availability.

To reassign a single segment

Click an assignment bar.

Select re-assign.

Select the resource selector.

Select a resource to re-assign the work to (you can also select an alternate project and sprint to move the work to).

Select re-assign.