How was this permission given? Was it a case of something popped up saying Dropbox "just once" or "always"? Those permissions are located in your app manager. You can go to the app manager, open the menu and select Reset app preferences which will do away with all of your associations, i.e. GMaps for map links, Chrome for internet links, etc. Or you can go to the app you've associated with Dropbox and reset it individually at the bottom of the app page by clearing the defaults. If you somehow linked the apps you will likely find the link information in the app you gave permission to. You may have to go online and log into the page for the app there to gain access to the this association. Not sure why but some times all of your options are not in the app. Of course if you would name the app you gave permission to here in your post you may get more specific information and possibly a step-by-step.