You initialize it out of the loop:
$referral_user_2 = new ReferralUser;
foreach ($referral_user_1 as $first_referral) {
$referral_user_2 = ReferralUser::where('referral_id' , $first_referral->user_id)->where('status' ,1)->get();
}
dd($referral_user_2); // you can access it out of the loop.
Btw, using ->get() will return a collection, not a single ReferralUser, you can use ->first() if you want to select just one.