If your campaign has a Form element by default or you have added a Form, you should have a submit button. If you happen to accidentally delete the submit/enter button, you can easily add it back. Here’s how:
In the Design section, click Add Form Field then select Submit Button.
The button will be added to your form and a slider menu will open to the left where you can edit the label on the button. Don’t forget to click “Save”.
In the left sidebar menu, you can click the six dots to the left of the field and drag up or down to reposition the button on the form, or use the “trash can” icon to delete the button.