I don't know what you mean by the term "wrongly arrested". If you mean that the cop arrested you on charges that you did not commit that's not what wrongful arrest is in the law. All the officer needs for an arrest is probable cause to believe you may have committed crime. That's not a real high standard. If you don't think the cop had probable cause then generally you challenge that in court in probable cause hearing (the name varies a bit from one state to another). You should have an attorney representing you in all phases of a criminal case. If you can't afford attorney fees, the state will appoint a lawyer for you. If you need/want to hire the lawyer yourself there are several ways to begin the search for the right attorney.
If you mean that cop used excessive force or otherwise violated your rights you may have a good civil rights claim to pursue against the cop and city/county that employs the cop. You'd want to contact a lawyer who handles civil rights lawsuits for that. But before you do that, talk to the lawyer handling the criminal case. You don't want something you do in a civil case to hurt your criminal defense.