"The action is complete, I want to close the form!"
Our advise: don't do it!
(That's why this option is not available via the interface.)
Even after a completed action, your landing page will remain a contact point for your supporters. They may have found an old link, or heard that the campaign was successful and looked for it!
If you simply close your form, you lose the opportunity to lead them to a different action or to add them to your supporter base.
Here are some ways you can deal with a finished action:
-> Convert your action to a simple newsletter subscription form
Amend the text to provide information about the result of the action. Ask people if they want to leave their email address, so you can let them know about upcoming and ongoing actions.
You might want to download the results of your form before amending it. If you delete form fields from your action, the related data gets deleted too.
Another option is to hide fields that aren't needed anymore - just set them to private and not required in the "Display" tab when editing the form.
-> Make a redirect to an ongoing action
Another good option is to set up a redirect to an ongoing action. For this go to: Manage > Advanced Settings > Site Settings and search for 'redirects'.
Be sure to redirect your supporters to a page where they not only learn about a new action, but also get information about the results of the old one. That's what brought them here and is interesting to them! So use this information to make the new action more engaging.
Of course, if you have another good idea and for this you need the form closed, drop a line to support and we can close it for you ;-)