Creating a direct link to your Google My Business review window can be accomplished in a couple of ways.
Generating reviews for your business shouldn’t be a painful process. Keep it simple, and show them how to do it.
Create a link from Google Search
Step 1. On your computer, search for your business using Google.
Step 2. Find your business listing and click Write a review.
Step 3. Copy and paste the URL you see in your address bar.
If these steps don’t work for you,
you’ll need to use the PlaceID Lookup Tool instead.
Create a link using the PlaceID Lookup Tool
Step 1. Go to the Google Places API.
Step 2. Enter your business name in the “Enter a location” field at the top of the map.
Step 3. Click your business name in the list that appears.
Step 4. Your Place ID will appear on the map, beneath your business name.
Step 5. Add your Place ID to the following URL after the equals sign to create your link:
https://search.google.com/local/writereview?placeid=place_id_goes_here
When customers click your link, they’ll be able to rate your business and leave a review. Learn how to read and reply to customer reviews

Handy Tip
Shorten your URL using bitly
Create a shortened version of the long code above and get the added benefit of setting up tracking on that particular link. Simply paste the long URL and click SHORTEN. Bitly will give you a shortened link that is easier to paste.
Like this sample. https://bit.ly/2t5RUKH
Now send to your clients and start getting Google reviews.