Hi @ShineVv0823
First of all, you need to have your SMS provider to get you a new SMS account as you can't mix marketing and transactional SMS accounts it will break the MO/SR processes
Then I hope you've been able to work with your SMS provider to align / get the information required by the marketing external account: critical elements such as Sending Windows, number of connection and hopefully you've also secured your Campaign configuration to add a SMS affinity. See documentation.
https://experienceleague.adobe.com/docs/campaign-classic/using/sending-messages/sending-messages-on-...
You would have to repeat all of these activities for the new account your SMS provider will give you and you create a new external account on the Marketing side with that information.
If the external account is not synchronised on the RT side as part of a template publication, you would have to provide the information to Adobe Customer Care that they can replicate the external account on the RT instance.
Also, you would have to explcitily require the SMS affinity to be setup on the RT instance...
Although this is not mandatory, it's best practice and a string recommendation to isolate the SMS deliveries from the other channels via affinity
Thanks
Denis