If you cannot login because you’re shown an error message saying “The message history has been encrypted. Please enter the encrypted password first” it is because you have decided to encrypt your message history.
This password can be different from your QQ sign-in password. If you have forgotten it, we won’t be able to help you reset it for security reasons.
As a last resort you can try to locate your QQ International installation path on your computer and look for a folder named after your account’s QQ ID. By deleting its contents you will be able to sign into QQ International again although you’ll lose all historical data and received files.