Okay, I think I've lost my setup key but I still have my phone and access to my codes.
Is-it possible to get back this key, or I must export to a new account ?
You can disable, and subsequently re-enable 2FA in order to get a new setup key.
First, you use a 2FA code generated by the authenticator app to disable 2FA. Next you enable 2FA on your account, the service will provide a new QR code and new alpha-numeric code that you need to load onto the authenticator app. This will be different than your previous code, and your previous 2FA codes will not work, so be sure to add this to your authenticator app. Before navigating away from the page with the QR code and alpha-numeric code, make multiple backups of this code in case you lose access to your phone.