You do not say how long it has been since conviction and sentencing. Based on the other facts you have presented, it seems likely the time to file a motion to withdraw plea has expired long ago but you didn't know that.
You likely will need to file a motion for postconviction relief which has a one year time limit. But you cannot do that if you still have a right to appeal. The time to file a Notice of Appeal runs from the date of sentencing and is 30 days long. So, if the 30 days is up and you have not filed a notice of appeal, you will be limited to review by postconviction motion.
I cannot recommend too strongly consulting with experienced Washington postconviction counsel about this case. You can find such counsel right here on Avvo by following the "Find A Lawyer" link at the top of this page.
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