While you can have any number of reviewers reviewing and scoring an abstract, the only people who can ultimately accept or decline a submission is an administrator.
To Accept or Decline a Submission:
Navigate within your event to Abstracts > Submissions
Tick the submission you wish to change the status for and click Change Status and select the status you wish to assign.
Do this for every submission Note: When you change these statuses, the notification email assigned to the new status will be sent to the Author.
When the page refreshes you will see that the status has changed. Any reviewers for this abstract will also see this change when they log in. This status is not permanent and can be changed by an administrator at any time.