The problem is in what your form_for @premails does when submitting it. Clicking the submit button on a form_for object will try to send the object either to the 'create' or 'update' action it's own controller depending on whether it's a new resource or not.
as the error message shows here you do not have a Premails controller. You either need to create a Premails controller with a create an update action or you need to change where the form sends the submit button to.
If you create the controller than in the create action you can redirect_to the about_page_path like this:
def create
@premail = Premail.new(premail_params)
if @premail.save
redirect_to about_page_path
else
redirect_to :back
end
end
Or if you dont want to create an entire premail controller you can change what the f.submit button does in your form to direct to an action in your pages controller. You would have to do something like
button_tag type: "submit"
The preferred method would be to create a premails controller.