The default sender ID is the identifier from which your messages will be sent. This can be either a random shared number, a specific dedicated number, or business name.
You will need to have previously purchased a dedicated number, or had an Alpha Tag approved and enabled prior to changing the Default Sender ID from the "Random Shared Number" option.
To update the default sender ID, go to Account and then Account Settings, and scroll down to Default Sender ID. Then click on the pen icon:
Next, just select the preferred option from the drop-down list and click Save:
Note - you can request Alpha Tags and Dedicated numbers, or add your own number by selecting from the options at the bottom of the drop-down list.
From now on, unless you manually change it at the start of the new message creation process, all your messages will be sent from this Sender ID. You can repeat this process to change the default Sender ID at any time.