Once a task has reached the In Review status it will be time for someone to review it. The Approval Plan field should indicate who the intended reviewers are.
By using the Approval Plan field, a 
To send something for approval, go into the relevant sub-task and fill out the description, including any checklists or links requested in the sub-task template.
If the reviewer has no comments they should mark the approval as “Approved”.
If they have comments or bugs to report, they should add their comments as subtasks of the original task (parent task of the approval subtask), not the approval subtask. They should mark the approval sub-task as “Changes Requested”. The approval sub-task should be used lightly instead of being a place where conversation occurs.
Once the responsible party has fixed the issues, they should comment back to seek approval again, and turn the approval status to “Pending Approval” (empty), and the cycle repeats.