As part of the process to add @charlotte.edu addresses to University email accounts, your default send as address will be changed to an @charlotte.edu address.
In the window that opens, type the address to add (ex. username@charlotte.edu address) in the Email address: field then click Next Step
Your name should already show in the Name field. The Treat as an alias checkbox should remain checked.
You will now see the newly added address (ex. username@charlotte.edu) listed in the Send mail as: section
If you already have your.alias@charlotte.edu as your default send as address, you will not be able to permanently set your username@charlotte.edu address to the default. The default send as address is administratively synced which will overwrite any change you try to make to your default send as address.