Hi Zaid - The Quality Administrator role includes a permission to delete completed evaluations. With that permission when you select the Evaluation Summary tab there will be an option to delete the selected evaluation.
*Attached is a screen shot of what that would look like.
At some point we'd like to add the ability to prevent multiple evaluations of the same recording. To help with issues such as disputes, completed evaluations can be re-scored.
Hope that helps you.
Lesley