[@robin-w Moderator 5 years, 9 months ago]

find
wp-content/plugins/bbpress/templates/default/bbpress/content-single-forum.php

transfer this to your pc and edit

find line 45

<?php bbp_get_template_part( 'form', 'topic' ); ?>

and delete this line and save

create a directory on your theme called ‘bbpress’
ie wp-content/themes/%your-theme-name%/bbpress

where %your-theme-name% is the name of your theme

Then transfer the file you saved above and put in in the directory called bbpress that you created above, so you end up with
wp-content/themes/%your-theme-name%/bbpress/content-single-forum.php

bbPress will now use this template instead of the original