Go to Account - Info and select Google Authentication.
Scan QR code or go to Google Play/App Store to download Google Authenticator in your phone.
Open Google Authenticator to Scan Barcode and generate new code.
How to add new Google Authentication:
Android: Click [...] to Set Account and Scan Barcode.
iOS: Click [+] to Scan Barcode.
Enter 6-digit Google authentication code, enter mobile captcha, and click Bind.
Note: When binding Google Authenticator, your private key is the ONLY mean of reclaiming Google account if your mobile phone is lost or replaced. Please save your private key as it shows ONLY once.