Trying to Get 3rd Mates License

Good afternoon. I’m new to gCaptain but have been reading some of the posts… very informative so I’m hoping someone can help me with a question.

How do I get my 3rd Mates?

I’m a SWO and have served as a Navigator for the last 2 years. I’ve been OOD qualified on 2 DDGs. I heard someone tell me that I have to get a transcript of sea service before I even start. Where do I get this from? How does this process work? Any assistance would be greatly appreciated!