How to rewrite mcrypt_decrypt function under PHP 7.4?

Question

PHP

The mcrypt_decrypt function has been deprecated since php 7.1.

private function decode3DES($enc_str)
{
    $key_hex = pack('H*', $this->secretKey);
    $data_hex = pack('H*', $enc_str);

    return mcrypt_decrypt(MCRYPT_3DES, $key_hex, $data_hex, MCRYPT_MODE_ECB);
}

How can I make it work on later versions of PHP?