How can I approve a form

I have my form set up with the Hidden radio field, but when I try to edit it and approve the request, I cannot approve it because it is hidden.

I can see you are using a form collapse and set it as hidden and closed, do note that this way the form collapse will never be shown in the form, what I would suggest you is to set the field directly as hidden then when you edit the submission in the submissions page. 

Here's a screenshot about how you can set a field as hidden: 

Here's also a guide about editing a submission on your submissions page, this will show you the hidden field so you can proceed approving or declining the submission: How-to-Edit-Submissions-Made-on-Your-Forms

Hope this helps.