BuddyPress.org

> Do you think you could tell me where exactly I should paste the code?

No. We don’t know what you’re trying to do.

But you definitely don’t want to paste it into a template.

You want to put it in theme functions.php or bp-custom.php

Maybe you want to run it once to handle existing users.

Maybe you want to run it in certain situations, for example on new registers:

function make_user_active( $user_id ) {
	bp_update_user_last_activity( $user_id );
}
add_action ('user_register', 'make_user_active', 1, 11);