How to close fields on a form?

When I edit a section or area on say an Optin form, how to I close that field or section that I just edited. I can open areas to edit but can't close them.

Are you referring to the pop-up window when you click the options or properties of the field? I wasn't able to replicate your issue. Please check my screen animation:

You can click the "X" on the upper right corner or just click anywhere in your form. Keep in mind to save the changes first before closing the window.

If I misunderstood your concern, please provide a screenshot of the issue so we can investigate it further. Thank you.