how do I add second touch ID?

Hey there rshalf,

If you're looking to set up a fingerprint on your Mac, use the steps below:

1. On your Mac, choose Apple menu  > System Preferences, then click Touch ID .

2. Click “Add Fingerprint,” enter your password, then follow the onscreen instructions.

If your Mac or Magic Keyboard has Touch ID, the sensor is located at the top right of your keyboard. You can add up to three fingerprints to your user account (you can save up to five fingerprints on your Mac).

3. Click the checkboxes to select how you want to use Touch ID:

• Unlocking your Mac: Use Touch ID to unlock this Mac when you wake it from sleep.

• Apple Pay: Use Touch ID to complete purchases you make on this Mac using Apple Pay.

• iTunes Store, App Store & Apple Books: Use Touch ID to complete purchases you make on this Mac from the Apple online stores.

• Password AutoFill: Use Touch ID to automatically fill in user names and passwords and to automatically fill in credit card information when requested while using Safari and other apps.

•Use Touch ID sensor for fast user switching: Use Touch ID to switch Mac user accounts.

For more details on using fingerprints, follow this link: Use Touch ID on Mac - Apple Support

Take care!