Activate buddyPress on alternate site

I’m SOS, stuck on stupid, and for the life can’t figure out how to activate BP on alternate site in a multisite network. I add “define ( ‘BP_ROOT_BLOG’, 2 );” to the wp-config file but only see the option to active on the main site. I activate it but don’t see anything on the /community site. I’m sure I’m missing something and could use some basic direction.