Rannko does not current support direct review responses from within the application. You can however click the "View Review", and this should take you directly to the review. From there you can respond to the Yelp review.
Yelp states the following below of how to respond to reviews.
How do I respond to reviews of my business?
If you have claimed your business page, you have the option of responding to reviews with a public comment or direct message to the user or you may send a quick thank you note to show your appreciation to the reviewer. If you've claimed multiple business pages on Yelp, you'll need to select the specific location from the lower left sidebar before following these steps.
Please note that we require business owners to have an approved profile photo and an approved business account user name to respond to reviews. We've found that reviewers are much more receptive to dialogue when they can attach a face to their interactions.
Instructions for:
To respond to a review via public comment
Go to the Reviews section of your business account
Locate the review and click Add Public Comment
Enter your text and click Preview
Review the text and click Post Comment
If you would like to edit or remove your comment, click on the overflow menu (three dots) to the right of the comment, and select Edit Comment or Remove Comment.
To respond to a review via direct message
Go to the Reviews section of your business account
Locate the review and click Send Direct Message
Enter your text and click Send
To respond to a review from the Yelp for Business Owners app
Tap Activity in the bottom navigation bar
Tap Reviews
Tap the review you'd like to respond to
Tap the bar at the bottom of the screen that says Write a response...
Write your response and tap Next
Preview the response. Toggle the Make Reply Public switch to ON if you'd like it to be a public comment on the business page (OFF will be sent as a direct message to the reviewer)
Tap Post