In a marketing action, it is possible to edit/modify an HTML via Sunflow or via a pro editor (with the same tools as Windows).
Editing a template is not the same depending on your HTML.
Indeed, if your HTML is an imported HTML (therefore an HTML pro) the modification is as follows (Cf. Editing/modifying an HTML template (pro)).
The modification of a template that you have created via Sunflow is as follows (Cf. Editing/Modifying a CRM360 HTML template).