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. 

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.
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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.
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​Instructions for:

To respond to a review via public 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.
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To respond to a review via direct message

To respond to a review from the Yelp for Business Owners app