That question recently came up on Quora (https://www.quora.com/How-do-you-correct-a-lawyers-mistake-without-risking-damaging-their-reputation).
I can’t give any better advice than Ken Dunham’s in this same thread, assuming you trust your lawyer:
“If you think your lawyer has made some sort of mistake, you should discuss that privately with your lawyer. If the lawyer has indeed made a mistake, they will be grateful for the opportunity to fix it. Or perhaps you’ve misunderstood the situation, and you’ve now given your lawyer the opportunity to help you better understand the reality.” (Ken Dunham, J.D. Law, University of Ottawa)
Even the most skilled, earnest attorney can make an honest mistake. These are the kinds of attorneys who would be grateful to have a mistake brought to their attention because they desire to do their best work for you, and if they’ve caused you inconvenience or even serious damage by a mistake of theirs, they would want to know about it as soon as possible, so that they could do all they could to fix it.
Other attorneys are either so self-serving and/or insecure that the last thing they’d ever do is admit a mistake. Indeed, rather than admit to a mistake they would choose to lie in an effort to cover the mistake (often at the client’s expense) and/or blame the client (falsely) for the mistake. They abuse their skills as attorneys to take advantage of clients. Those are the kinds of attorneys for whom it does no one any good to worry about protecting their reputations. Those are the kinds of attorneys who don’t deserve your concern for their well-being because they don’t care about yours. That does not mean you should abuse, exploit, or blackmail that kind of attorney, it means you should be on your guard to protect yourself from that kind of attorney protecting his/her reputation at your expense.