Successful appeals must present a specific legal problem with the plea that you entered voluntarily and which was approved by the judge. An appeal is taken by filing a motion for new trial in the court where you pled guilty. The motion must be accompanied by an affidavit that outlines the specific facts that form the basis for your appeal. The affidavit should be signed under the pains and penalties of perjury by someone who has personal knowledge of the facts stated.  

If you are successful, the case is not dismissed, instead you get a "new trial". It will be as if you did not plead guilty and the case starts over.

Talk to a lawyer to learn more about your options to appeal and the process that must be followed.