$update_id = segment(3);

$data['update'] = date('Y-m-d');
$dse_instrument_id = $this->_get_instrument_id($update_id);
$this->model->update($dse_instrument_id, $data, 'dse_instruments');
$data = $this->_get_data_from_post();
$this->model->update($update_id, $data, 'dse_financial_keys');

echo '$update_id = ' . $update_id . ' (' . gettype($update_id) . ')<br>';
echo '$dse_instrument_id = ' . $dse_instrument_id . ' (' . gettype($dse_instrument_id) . ')<br>';
json($data, true);

$this->db->where('dse_financial_key.dse_instrument_id',$instrument_id);
$this->db->update('dse_financial_key', $db_array);

function _get_instrument_id($update_id){
$result = $this->model->get_one_where('id', $update_id, 'dse_financial_keys');
//json($result);die();
$instrument_id = $result->dse_instrument_id;
return $instrument_id;

}

if ($result == TRUE) {
$update_id = segment(3);

$data['update'] = date('Y-m-d');
$dse_instrument_id = $this->_get_instrument_id($update_id);
$params['id'] = $dse_instrument_id;
//json($dse_instrument_id);die();
$sql='UPDATE `dse_instruments` SET `update` = `'.$data['update'].'` WHERE `dse_instruments`.`id`=:id';
$this->model->query_bind($sql, $params, 'object');
//$this->model->update($dse_instrument_id, $data, 'dse_instruments');
$data = $this->_get_data_from_post();
$this->model->update($update_id, $data, 'dse_financial_keys');
$flash_msg = 'The record was successfully updated';

}

private $debug = true;

//QUERY TO BE EXECUTED:
-> UPDATE `dse_instruments` SET `update` = `2022-05-03` WHERE `dse_instruments`.`id`=2
//PLEASE NOTE: The query shown above is how the query would look before binding. PDO currently has no means of displaying previous query executed.

//providing the data passed above equals this:
$dse_instrument_id = 2; // just a number I pulled out of my ass, as you did not share it's value
$data['update'] = '2020-05-03';

$update_id = segment(3);

$data['update'] = date('Y-m-d');
$dse_instrument_id = $this->_get_instrument_id($update_id);
$this->model->update($dse_instrument_id, $data, 'dse_instruments');
$data = $this->_get_data_from_post();
$this->model->update($update_id, $data, 'dse_financial_keys');