I’m leaving in a week for Navy Boot Camp and then A school for MA. How do I go about doing the Harbor Patrol Unit?

Boot first, recruit. Then A school. THEN worry about where you wind up. In Boot, your goal is to NEVER have the company commanders know your name by heart. Good luck and congrats on your decision to serve. Having said all that, if harbor patrol is your desire, you'd have been better off in the Coasties.

SR (Join to see) I agree with MSG (Join to see) Your job ahead of you is to learn as much as you can and excel in Boot Camp. Once you accomplish that, you need to do the best that you can at Master At Arms training. It is great to have long range goals, but do not get ahead of yourself.

https://www.military.com/join-armed-forces/navy-boot-camp-schedule.html

https://www.thebalance.com/navy-enlisted-rating-descriptions-qualifications-3345832

While not Navy (clearly), my recommendation is for you to focus on the steak and not the peas. Right now your focus should just be getting thru Boot Camp. Once that's done, then your focus should be getting thru MA school.