Hello, We understand it can be frustrating changing carriers, especially during a Beta. These are the steps to withdraw from the Beta:
1. To withdraw from the One UI Beta Program, you must apply for withdrawal through Samsung Members application on your device. ("Settings > One UI Beta Program status > Withdraw" menu)
2. To remove the beta software, perform a rollback to the previous release version, using the Smart Switch application on your computer. The rollback resets the device and removes data generated during beta testing.
Note: If you backed up your device data to your computer with Smart Switch, you can restore the data after the rollback process. To perform the rollback, connect the device to your computer with a USB cable. On the computer, launch the Smart Switch application, and select "Downgrade".
If you do not have access to a computer and need to roll back your device, contact the nearest Samsung Service Center. https://www.samsung.com/us/support/service/