Admins have permission to mass end goals and mark them as incomplete.
Step 1: Navigate to the Goals page.
Step 2: Select your filter of interest within the Goal Explorer.
Step 3: Ensure you are in the list view.
Step 4: Complete the goals by selecting End Displayed Goals.

Please note: the goal progress will remain the same. For example, if a goal displays 75% completion, it will remain at 75% even if you end it.
All goals selected will be marked as Incomplete. Learn to reactivate an ended goal in How to Reopen an Ended Goal.