In order to use quick replies, in your main inbox list view please swipe the mail to the right | Select ‘More +’ | Quick Reply (at the bottom)
You can also quick reply when viewing an email by tapping the 3-dot menu in the bottom right corner | More Actions | Quick Reply.
Afterwards, you’ll be prompted to “Insert Quick Reply” and can use one of the many quick replies available on the list.
To edit or add a Quick Reply, please tap *o o o* | Global Settings | Customize Menus | Configure Quick Replies.
Note: You can also use Quick Replies Directly from the List View.