You are under a fundamentally wrong assumption: The content you input via the administrative back-end does not live in a file, but in the database, specifically in the wp_posts table.
Do not be misguided by the table’s name, a “page” is technically a post of type page.
If you attempted to find the content you created via your “hosting file manager”, it is very likely your hoster also provides you with a tool to explore your database – In 90+% of cases, that’ll be “phpMyAdmin”.