How to update account when user don't want to update all database field

Below is my Controller method for letting users update their details.

I am using ion_auth to update the details, but it's simply a Model wrapper.

PHP Code:

   public function index()
    {
        $this->form_validation->set_rules('username', 'Username', 'trim');
        $this->form_validation->set_rules('first_name', 'First name', 'required|trim');
        $this->form_validation->set_rules('last_name', 'Last name', 'required|trim');
        $this->form_validation->set_rules('telephone', 'Telephone', 'trim');
        $this->form_validation->set_rules('email', 'Email', 'required|trim|valid_email|callback_new_email_is_unique');
        $this->form_validation->set_rules('new_password', 'New password', 'trim|xss_clean|matches[confirm_new_password]');
        $this->form_validation->set_rules('confirm_new_password', 'Confirm new password', 'trim');

        $this->form_validation->set_rules('twitter_username', 'Twitter Username', 'trim');
        
        if ($this->form_validation->run() == FALSE):
            
            $this->data['message'] = (validation_errors()) ? validation_errors() : $this->session->flashdata('message');
            
            $this->load->vars($this->data);
            $this->load->view('account/index');
        else:
            $data = array(
                'first_name' => $this->input->post('first_name'),
                'last_name' => $this->input->post('last_name'),
                'telephone' => $this->input->post('telephone'),
                'email' => $this->input->post('email'),
                'twitter_username' => $this->input->post('twitter_username')
            );
        
            if($this->input->post('new_password') != '' && $this->input->post('confirm_new_password') != ''):
                $data['password'] = $this->input->post('new_password');
            endif;
        
            if($this->ion_auth->update($this->user->id, $data)):
                $this->session->set_flashdata('success-message', 'You have successfully updated your details.');
            else:
                $this->session->set_flashdata('error-message', 'Oops, something went wrong. Please try again.');
            endif;
            
            redirect($this->session->flashdata('referrer'), 'location');
        endif;
    }