What's your ColorOS version? If you've the 5.0 version or above, you can reset your password by tapping Forgot passcode, then answering your security questions or using your security email address.
If you don't have access to your security email address or forgotten your security questions, you'll unfortunately not be able to reset your password.
In this case, in order to reset the File Safe password, you'll need to perform a factory reset of your Oppo phone. By doing this, all your data will be permanently erased, so don't forget to backup your data!