@Hannah417
If you click on 'Performance' on the top bar of your listing first.
Then select 'reviews' ; Here you can select the review you wish to reply to
Select 'read review' and then you should see the 'reply' button.
Top caution on replying though, is it damp smell and spotty wifi girl you want to reply to?
Conventional wisdom says ; keep it brief, professional and don't go settling scores, write as if you addressing 'dear potential future guests' and not to the reviewer.