Unfortunately, there’s no setting to show the popup again after X number of days.
You can set a cookie so the OptinFire Popup will show only once after the user closes it, to do this you need to:
1. Edit your Optin
2. Click on Display Conditions
3. Check “Don’t Show Again” on the Display Location section.
Also on that same settings page, you can set a date range for your Optin, so I have a suggestion for you:
1. Limit the date range to 30 days
2. Go back to All Optins
3. Hover over the Optin you just edited and click on Duplicate (looks like a copy icon)
4. Edit the duplicated Optin
5. Set the date range to show after the 30 days
This way it will show up again after 30 days for users who closed it, hopefully this will work for you.