As the Org Admin you can change or delete existing mail approval configurations.
You can’t remove an approver when a mail approval is marked as Pending.
Mail approvals can be set at an Organization or Project level, but only apply to your organization. You cannot approve mail sent from other organizations.
If you see the word 'Pending' in the Remove column, you'll need to contact one of the Approvers to Approve or Reject the pending mail. Once all mail approvals are cleared you can then remove the configured mail approval.