Step 1. Once you are inside a particular review's detail page, you'll see a card towards the bottom of the page:
Step 2. Click Copy and send that link to the customer
Your customer then, will:
Step 1. Go to a page which is branded in your store's logo where your customer can enter. An example is like below:
Step 2. Then your customer will enter their email address. It's important that this email address is the same one that belongs to the review to be edited.
Step 3. Your customer will receive an email shortly, after entering the email address and hitting Continue button.
Step 4. When your customer clicks the button inside the email, the customer will go to an authenticated page and see all the reviews that they have left so far, for your store. She/he can choose any of them and edit them easily. Everything about the review is editable including rating, content and photos/videos.