If a submission has already been reviewed by one of the coaches, you cannot remove the submission from your list of 'To Review'. At this time, there is no functionality that allows you to clear out multiple Coaching Activity Approvals at once. You would need to either delete those courses or make the courses inactive in order for the pending reviews to not show in the Activity Reviews view.
If you would like to request this functionality, you can do so in our Product Suggestion Forum. For more information about this process, you can click here.
If you need additional assistance, please contact Support.