You can make three types of changes to resource assignments:
You can add more resources to the existing resources assigned to a task.
You can replace one resource with another.
You can remove a resource from a task.
To add more resources to the existing ones initially assigned to a task, follow these steps:
In the Gantt Chart or other task sheet, click the task to which you want to add more resources.
On the Standard toolbar, click Assign Resources. The Assign Resources dialog box appears, showing a check mark next to the names of resources already assigned.
You can also open the Assign Resources dialog box by pressing Alt+F10.
Click the name of the resource you want to add to the task and then click the Assign button.