In order to remove a Reviews from a submission you will fist have to navigate to the Reviewing tab.
From there click the Review button circled below.
This will bring up all the reviews for the project.
You can Filter the list in order to find the review you are after quickly.
There are four filters you can use:
Submission number: Type in the reference number of the submission with the review you want to remove.
Reviewer: Type in the Email of the reviewer who wrote the review you want to remove.
Status: choose the status of the submission.
Score: choose the score that the reviewer set.
Now you can tick the boxes of the reviews you want to delete.
Then you simply click Delete Selected Reviews.