1. Go to Settings → Account.
2. Select Enable two-factor authentication. Then, fill in your current password and click "continue".
3. Scan the QR code with an authenticator app (e.g. Microsoft Authenticator, Google Authenticator or 1Password).
4. Enter the 6-digit code to confirm.
5. Save your 8 recovery codes in a safe place.
Each recovery code works once. Use one if you lose access to your authenticator app.