If you open the file in your web browser, it’ll have a url like https://SITENAME/uploads/default/original/3X/9/3/9366a9b417a1d94f0a8482f7835.odt
If they have a standard install, they would then delete
/var/discourse/shared/standalone/uploads/default/original/3X/9/3/9366a9b417a1d94f0a8482f7835.odt