what action can a defendant take after being misrepresented in a criminal trial

You can complain to the bar association, sue the attorney for malpractice and/or get a new attorney and try to get a new trial. Whether you can get a new trial depends on how long ago the conviction was so move quickly to get another lawyer involved.

You have not provided enough information to give you any intelligent response. Try again, please.

Mr. Dinday is correct, your question lacks information. Nevertheless, some additional actions that can be taken are: complain to state bar, gather evidence to support attorney's misrepresentation (transcripts of hearings, declarations from opposing/co-counsel, letters or notes written by this attorney), seek help from another (trusted) attorney. Move fast, because there are deadlines to overturning convictions. Good Luck

Your question does lack a little detail, but suffice it to say you need to move quickly. Convictions are difficult to overturn so you will need to follow the advice of the other posters. Good Luck!