To send an app review request for iOS 10.2 and earlier or Google Play (Android app store), create a new in-app message and select the Confirm template.
Note: If you want to send a request for iOS 10.3 and up, see here.
Set up the message's text with your custom rating request, and change the text of the Accept and Cancel buttons to fit your rating message.
Set the Accept action to "Open URL" and paste in the link to your app's review page in the App Store. The cancel action should be "No action," or you can chain to another message or link asking for additional feedback.
Note: If you are also sending review requests to users on iOS 10.3+ with the new app review prompt, make sure the 10.3+ message's target includes 'iOS version 10.3 and above.' Also make sure your target for the 10.2 message includes 'iOS version 10.2 and below.' This will prevent users on different versions from receiving conflicting or duplicate versions of the same message.
For an example of an effective app review request message flow, see How to get more five-star app reviews.