Hi,
What you want to obtain is not just a basic setting in bbPress that you can switch on. It requires changing one of basic php files. As the golden rule is to never change any bbPress files directly, there are different ways of coming to what you want, in this case it would be copying the file from the bbPress folder/directory and modifying it. Information on creating a child theme can be found on the codex: https://codex.bbpress.org/functions-files-and-child-themes-explained/
Hope that helps,
Pascal.
