If you need new passcodes, there are multiple ways you can request them.
Using Backup Codes in CalNet Account Manager
Log in to your CalNet account with your usual credentials
When you are prompted to do a 2-Step, "Text message passcode" will show up if it is the default 2-step choice. If it is not the default, when prompted to enter your credentials, select "Other options." You will be taken to a page with other verification options. Select "Text message passcode".
Then, check your cell phone for a text message with a single use passcode and enter it in the field, and press verify.
On your phone, go to Duo Mobile. Tap the entry that says "CalNet - UC Berkeley" to view a passcode. This works anywhere, even in places where you don't have a WiFi connection or can't get cell service.
To receive a text message with 10 passcodes, go to mycalnet.berkeley.edu and log in to the CalNet Account Manger. Select Manage My 2-Step on the left menu. Then, when you are presented with the Device Control Panel, click into the box that says Enter a Passcode. A blue line will appear at the bottom of the Device Control Panel that has a link to "Text Me New Codes." Click the link and check your text messages for a set of single-use passcodes.
You can also request passcodes by logging in to the CalNet Account Manager and selecting "Get Backup Passcodes" at the bottom of the Device Control Panel screen.
To use these backup passcodes to authenticate, log in to your CalNet account with your usual credentials.
Once the Duo screen is prompted showing your default device choice, select "Other Options" located at the bottom.
Then, select "Bypass code" located toward the bottom of the list of verification devices.
Enter one of the backup codes you received earlier from CalNet Account Manager into the field below, and click verify. You're done!
Note: Passcodes are single-use only; you must enter a new passcode each time you verify.