You can assign the SIDs to other sub-accounts by following the below screenshots:
1. Click on The Menu Icon.

2. Click on Account Settings.
3.Click on Teams and then navigate to Manage Teams as shown below in the screenshot.
4.Click on Manage Team.
5.Please follow the below Steps: -
Click on Team Duties
Select Applications and Communications APIs
Assign SMS Sender ID
In the SMS Sender IDs section, choose the desired Sender ID from the dropdown menu.
Click on Save Changes.