First you should install a fresh wpForo on sitie2.com.
Make sure the 1 and 2 websites table prefix is the same (e.g.: wp_ )
Then backup wpForo tables with DROP TABLE command (all tables with wpforo_ secondary prefix, e.g.: wp_wpforo_... ) from sitie1.com and import to sitie2.com database.
If the target WP ( sitie2.com ) has more than one user you can't do this migration. You should ask Migration Services. UserIDs are unique, and you can't import sitie1.com website users to sitie2.com website users table. If you can't migrate users then forum can not be migrated too. wpForo is based on WordPress users table. if you move wpForo tables to new WordPress website the user IDs will be changed. The easiest why to migrate wpForo tables with _users and _usermeta table. In this case you just need to migrate tables, and all will work fine, but the WordPress admin login details will be changed to sitie1.com admin login details.
However this is not a simple task. Forum to Forum database migration services provided by specialized teams like ProfProject or gConverter.