You can easily disable submissions on any form. Under Configure → Form Behaviour → Form Availability there are several options to configure when submissions should be closed.
Simply turns off the submissions of the form manually.
Disable after a maximum number of submissions
When the form hits the specified number of submissions, then submissions will be closed automatically.
Submissions open after date/time
If the current time is before the specified date and time, then submissions will be closed.
Submissions close after date/time
If the current time is after the specified date and time, then submissions will be closed.
If any of the above options are met, the form’s submissions will be closed.
When the submissions are closed, by default a message is displayed saying “Submissions are closed”. This text message can be changed using a custom translation.
On Pro and Agency plans, you can also create a custom closed submissions page by toggling on Under Configure → Form Behaviour → Custom Closed Submissions Page in the form editor, then clicking and editing the message. Editing the custom closed submissions page is just like editing a form (click and type, select text to change headings, insert images, videos etc).