[@robkk Moderator 11 years, 11 months ago]

you can use any of these hooks to add a button there using a function

add_action( 'bbp_theme_after_topic_subscription_action' ); 

add_action( 'bbp_theme_before_topic_subscription_action' ); 

add_action( 'bbp_theme_after_topic_favorites_action' ); 

add_action( 'bbp_theme_before_topic_favorites_action' ); 

more info on using action hooks

Step by step guide to setting up a bbPress forum – part 4