Who do I contact regarding missing information on DD214 (Navy Achievement Medal)?

Since it was 30 years ago, you'll have to submit a request to the Board for Correction of Naval Records*. You can submit an application online, but understand it's usually a lengthy process (but, you have been waiting 30 years already...)
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* https://www.secnav.navy.mil/mra/bcnr/Pages/default.aspx

I’ve tried to get the Navy Commendation Medal added but had no luck. It’s been forty years so I’ve never displayed one in by shadow box. I ETS’’s the same time it was supposed to be awarded so I figured command never followed through. I hope you have better luck Cpl Josh King

The DD 214 is only the record of service. If you have the orders or certificate for the award then you may not need to add it. It is good to have all of your awards on your DD214 but I don't know of a situation where a missing award on a DD214 would hinder you. I would still display it in my shadow box.