If you have been granted a subclass 491 visa, you must hold the visa for at least 3 years before you can apply for a subclass 189 visa.
However, there is a catch! You can still apply for subclass 189 by going overseas on 491, requesting visa cancellation, and then lodging 189 if all this can be done within 60 days of your 189 invitation.
If you need Immigration assistance get in touch by making an appointment for a phone/video consultation or ask for a written consultation.