I’m just a user but I think you need to create a new template in your theme (or child theme) directory called single-user.php
If you have that then the user profile page will use that template.
You can find an example of this template in /wp-content/plugins/bbpress/templates/default/extras
To do this I would:
- Create a child theme of my current theme if I did not already have one.
- Create a sub-folder in there called bbpress.
- Copy the single-user.php file from /wp-content/plugins/bbpress/templates/default/extras into my new /themename/bbpress folder.
- Edit the file.
This template also calls other parts from /wp-content/plugins/bbpress/templates/default/bpress which you might also want to modify, in which case you would also copy some other files across for editing. I think it calls content-single-user.php which then calls user-details.php etc.
