Can you say more about what you’re doing? What are you changing with the form? Can this be a theme component? Is what you’re submitting to an existing endpoint or one that you’re adding?
See Discourse toolkit to render forms
Then you can get GitHub - discourse/all-the-plugins and grep for “<Form” but you can also see Code search results · GitHub as described in Discourse toolkit to render forms - #20 by david (though those are all in core, not plugins)