Your SCUM account is linked to the third-party platform that you use to play through. If you don't have access to the registered email address, you'll need to recover your third-party platform account that your progress is on.
Steam | Recover your account
If you have access to the email address or phone number registered to your account you can request a password reset to log back in.
If you don't know the email address or phone number you'll need to contact Steam customer support directly to get assistance.
For more information, head to this guide on recovering a lost Steam account.
I still can't access or recover my account. Can you transfer my progress to another account?
Due to technical limitations, it isn't possible for us to transfer progress between accounts, even if you've lost access to your current account.
If you are unable to recover your account you will need to create a new account to continue playing: