Can not read MMS on dual SIM phone
If you don't have data service at all on your secondary SIM, you can't download the SMS. Since the SIMs are from different carriers, the primary SIM can't connect to the other carrier's MMS service, and therefore the message can't be downloaded.

The only solution would be to replace your primary SIM with the secondary one, establish a data connection and download the MMS. Otherwise you can't download it.