A little late, if you are still looking for help or if someone else is looking for similar information.
Usually you would create HTML on options pages by specifying a function to call in either add_options_page or add_submenu_page in WP. But you can’t include a function to call when using ACF options pages because ACF sets this function to its own function that adds ACF custom fields to the option page.
The best option here is to use a message field at the top of your field group to give detailed instructions.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users