Make user author

author-role.php

add_action('bp_core_activated_user', 'bp_custom_registration_role',10 , 3);
function bp_custom_registration_role($user_id, $key, $user) {
   $userdata = array();
   $userdata['ID'] = $user_id;
   $userdata['role'] = 'author';
   
   //only allow if user role is my_role
   if (($userdata['role'] == "subscriber") or ($userdata['role'] == "contributor"))
      wp_update_user($userdata);
  }