It is likely that the time for any direct appeal has expired in the case. However, you might have some recourse through what is commonly referred to as a habeas corpus petition. You will need counsel who handles post-conviction work. These cases can be expensive because they require investigation of events that took place many years ago. Sometimes you can petition the court for appointed counsel, although there is no right to appointed counsel on such a petition. You also might consider contacting the California Innocent Project to see if they have any lawyers who would handle the case pro bono.
You need an attorney that handles appeals. This is specific niche area that attorneys will specialize. Based on the length of time that has passed, it is likely an appeal is not available. However, if you consulted a lawyer that does criminal appeals...they could better advise.