The customizer, as it is mostly for style settings.
If you want to make a heading dynamic then you could create a custom field. Then echo that into the page or post template using the get_post_meta function, and wrap it in whatever HTML tags you wish.
Hope this helps!
check these out:
https://wordpress.org/support/article/custom-fields/
https://wordpress.org/support/article/custom-fields/#displaying-custom-fields
Or you could try these plugins: