AxCrypt 2 will use the account and password you originally registered with AxCrypt 1 – possibly a long time ago.
If you do not remember the password to your account, you can always reset it. This is not a way to recover encrypted files! It’s only to allow you to sign in to the AxCrypt app and web. The new password will be used to encrypt new files. Go to https://account.axcrypt.net/Home/PasswordReset to do this, or you can also go there from AxCrypt with File | Options | Password Reset .