Some of them when you click the select box then edit at the bottom you have an option to edit the dates for the actual and next review. Many if them dont have the option to edit them so i have items in the Asset risk section that have past due review but i cannot edit the dates of the review to fix them
you probably need to learn how to implement and in particular use the policy module, check this video is all explained in detail.
when a review is completed you can no longer edit them.