Tether supports Two-Factor Authentication using the Authy app. You can find more information on the Official Authy Website.
In order to set Two Factor authentication up:
1. Go to Settings > General tab > Two-factor authentication
2. Choose Authy from the dropdown followed by "Update" to save the changes.
3. You will be redirected to the verification page:
4. Enter your phone number and click Register
5. Install and launch the Authy app on your phone. If you did not receive a download link, you can download Authy here: Download Authy
6. Click "I've opened Authy application"
7. In the Authy app, open the Tether tab. You will see a code which you need to enter on the Tether platform to login.
8. Enter the code and press Verify:
9. Now, every time you log in from a new device, you will be asked for this verification which you can obtain at any time by opening the Authy app.