Regardless of what password you set when you signed up this time, the old password is still the one you need to know.
If a file is encrypted with a different password than what you’re signed in with, it’ll ask you for the file password.
You can’t reset a password for encrypted files, that’s not how encryption works. You can reset the sign in password, but that only allows you to sign in to the service – it won’t let you open older encrypted files. To open or decrypt an older file you need to know the original password.