[Plugin: Custom Contact Forms] Custom HTML

I would like to use the custom HTML feature to write my own forms instead of going through the entire create-form / create-field process multiple times. I can’t see how to submit the contents of the custom form — there is no submit button in that section. Is this a bug, or is there some other procedure for using a custom (hand-written) form ?

https://www.ads-software.com/extend/plugins/custom-contact-forms/