If a Reviewer has not yet responded to a request, users with relevant permissions can remind them with an email prompt to complete their Review.
In the Workflow Request List (in your 'Workflow' or 'Approvals' tab) select the dropdown menu for the relevant request and select Send Reminder:
You will then be able to select which Reviewers you wish to send this reminder to.
You may need to remove users who have already submitted their Review and do not need to be reminded.
Note that for Staged Workflow requests that only Reviewers of the current stage will appear to send the reminder to.
Add a message to the user/s and click Save to send the Reminder/s.
* Please note that some of the terms used above such as Workflows & Approvals are customisable and may appear differently in your platform.