You can change your Default Account using More | Global Settings | Advanced Features:
- Default Account when Launching App – Which account will be displayed when you open TypeApp.
- Unified will show your Unified Inbox.
- Last Visited Account will show you the account that was in use the last time you’ve used TypeApp.
- Default From in Unified Inbox – From which account your new email will be sent.
In addition, you can also change the From Address by tapping on it within the compose screen and choosing another address.