The Ultimaker Account supports two-factor authentication using an app that generates one-time codes. If for some reason you no longer have access to this app you can follow these steps to regain access to your account.
1) Use a backup code
During the two-factor authentication setup flow you were asked to copy or download a set of 10 backup codes to a secure location, for example a password manager. You can use one of these codes instead of the generated code from the app. You can use each backup code only once, so it is advised to completely reset two-factor authentication if you're running low on backup codes.
2) Create a support ticket
If you lost the backup codes or forgot to store them during the initial setup, you can open a support ticket with Ultimaker and you'll receive a manual reset code via email. A backup code is only valid for 1 sign-in attempt, so you must use it to navigate to https://account.ultimaker.com/app/security and reset two-factor authentication on that page.
Note: Signing in with a backup code does not automatically disable two-factor authentication.