First of all, follow the steps outlined in the article below if you have not as yet set up approver and reviewer reminder emails: 

• How to set a number of reminders for policy reviewers/approvers

Once this has been actioned, reminders will then be sent, on a weekly basis, to your approvers and reviewers up until the 'Approval Due Date' that has been set within the policy. 

• If the 'Policy Due Date' has lapsed before the first scheduled weekly reminder is due, then a reminder will not be sent. 
• Reminders will only be sent if the policy due date has not passed.