Settings for Captchas are set in Settings > CAPTCHA.
Choose the Captcha in Default Captcha – this opens a list of all Captcha. Then set the difficulty of it.
You can also preview the Captcha.
For QR/NFC Captcha, you can learn the code for recognition by tapping the “learn” button in Settings.
For changing the QR/NFC Captcha, tap on Settings below Preview, and then tap “learn” button. You can also delete the old code by tapping the trashcan icon in the same screen.