He didn’t withdraw anything he filed a motion asking the court to allow him to withdraw his guilty plea. And I’m not certain this is even the best strategy for him. We will see.
If Flynn believes he’ll get a pardon from Trump after the election - which I think is likely - then anything that delays the moment he has to go to jail is a good thing. If the judge agrees to let him withdraw the plea agreement, a trial would push back sentencing months even if he is convicted.