As of right now, the only way to merge a co-applicant is a work around. You have to copy a phone number or email address and then go to the primary application and paste it in. Then you have to go back to recall and paste the number or email back into its field to populate all 3 or more files. From there you can merge the files.
All we need is the check box for app and co-app. It's currently only on the main applicant.