How to Update Related Models in Laravel

Here in this documentation Laravel Inserting Related Model there is no method to update the current related model. Have a look: Relation Between two Models

 private function UserToken($token,$expire,$user_id){

     if($JetUserPass=JetUserPass::find($user_id)->token){
          $JetT = new JetTokens(['id_token' =>$token,'expires_on'=>$expire]);
          $JetUserPass2=JetUserPass::find($user_id);
          $JetUserPass2->token()->save($JetT);//NOT WORKING

    }else{
           $JetT = new JetTokens(['id_token' =>$token,'expires_on'=>$expire]);
           $JetUserPass=JetUserPass::find($user_id);
           $JetUserPass->token()->save($JetT);
       }
    }

via Chebli Mohamed