How to decrypt an encryption used with codeigniter library from the database?

We are implementing a register and login module for our project, my teammate used the codeigniter encryption service $this->encryption->encrypt($this->input->post('passw')) for our password. The problem is with our login, we can’t seem to decrypt or read it. Little help?

Login function in controller:

> public function log_validation()
    {
        $this->form_validation->set_rules('emp_id', 'emp_id', 'required');
        $this->form_validation->set_rules('passw', 'passw', 'required');
    
        if ($this->form_validation->run() == FALSE){
            echo "<script>alert('Login Error!')</script>";
            $data['title'] = 'Login';
            $this->load->view('include/header', $data);
            $this->load->view('user/login');
        }
        else{   
            $empid = $this->input->post("emp_id");
            $password = $this->encryption->decrypt($this->input->post('passw'));
            $key = 'mykey';
            $decryptpass = $this->encryption->decrypt($password, $key);

            //function in model to get employee id and password 
            $emp_ref = $this->Users_model->verify_employee($empid, $decryptpass );

            if($emp_ref == NULL){
              echo "<script>alert('Member not found')</script>";
              redirect('Users/login_user', 'refresh');
            }elseif($emp_ref[0]->col_role == 1){
              $this->session->set_userdata("emp_id", $emp_ref[0]->col_emp_id);
              redirect('Users/dashboarda', 'refresh');
            }elseif($emp_ref[0]->col_role == 2){
              $this->session->set_userdata("emp_id", $emp_ref[0]->col_emp_id);
              redirect('Users/dashboard', 'refresh');
            }elseif($emp_ref[0]->col_role == 3){
              $this->session->set_userdata("emp_id", $emp_ref[0]->col_emp_id);
              redirect('Users/dashboard0', 'refresh');
            }
        }
    }

the model there is:

    public function verify_employee($empid, $password){
    $this->db->select('col_role, col_emp_id, col_password');
    $this->db->where('col_emp_id',  $empid);
    $this->db->where('col_password', $password);
    $query = $this->db->get($this->tbl_management_accounts);
    if($query->result() == NULL)
    {
        return NULL;
    }
    else
    {
        return $query->result();
    }
}