Update instead insert

I have tried to organize your coding a bit and asked you a question within the code area below. Could you please check?

PHP Code:

if($this->validate($rules)){

              //$post = $this->request->getPost();

              // generate random hash for email verification (40 char string)
              $user_activation_hash = sha1(uniqid(mt_rand(), true));

              $user_activation_hash = $this->$this->request->getVar('user_activation_hash');
              $id_stato_users = 1;
              $tipo_utente = 1;
              $rand = rand(0, 999999);
              $pin = str_pad($rand, 6, '0', STR_PAD_LEFT);

              $data = [
                 'user_activation_hash' => $user_activation_hash,
                 'id_stato_users' => $id_stato_users,
                 'tipo_utente' => $tipo_utente,
                 'pin' => $pin
               ];
              
               $res=$this->UserModel->save($data); // rename your model please. Name should be capital

                $id_user=$this->UserModel->getInsertID; 

              log_message('debug',"post_id_user " . $id_user);

              $res2=$this->DentistiModel->save($data); // Why saving the same data for a different model?