How do I start the process of resigning my commission?

Try this link for insight:

https://work.chron.com/request-resign-national-guard-officer-commission-25082.html

are there no other options for you in your unit? is it due to harassment or something of that nature? I would hate to see an officer who has put in the time and effort to become commissioned give it all up. please understand that I do not expect you to reply as I am not trying to pry into your business. I would seek counseling with other officers who you could confide in to determine if you had other options other than resigning your commission. you have put in the time and it would be a shame to give up the time that you worked so hard for that will benefit you in the future. I once again urge you to talk to current or past military leadership (friends or family). I wish you the best in whatever you decide.

My Best Friend was in the US Navy, was commissioned and rose to the rank of LT or something like that. US Navy Officer ranks are a bit odd to me as I was US Army and US Air Force Reserve so their ranks were the same. My Best Friend gave up his commission as he was in the process of being deployed for a two + year period. Not a big deal if you are single but he had just married and did not know if he could trust himself at the many different ports of call around the world. He also came up through the Enlisted Ranks so knew from experience what can and usually does happen over time. Fast forward to today; He now regrets giving up his commission as he would have been retired with a nice monthly paycheck. I do believe that you should make your decision based on your gut feelings but give a lot of thought to your future. I know that it is no ones business to pry out of you any details about why you wish to give up your Commission, but you should get some counseling from the US Navy JAG or legal staff to hear your case. I would guess that you have a lot more years before you can consider retirement but I think you are making a hasty decision based on something that is clouding your thoughts and guiding you at this time. Who knows in six months or a year from now everything changes. I do hope that you make the right decision for the right reason. Just my two cents for what it is worth! I do wish you all the best and hope you are able to obtain what you wish. ;-) I Salute All My Fellow Veterans!!! GOD Bless America!!!

Possible, probably but I have a feeling there's an underlying issue that wouldn't be solved by reverting to enlisted.

I saw a little of your reasoning in the comments below.
I spent 5 years working my butt of to get my bachelors as a line NCO, only to be turned down for a chance at OCS because I was 3 months past 10 years of service. You did the work to become an officer, don't throw it away because of a temporary situation.
You are in a unique position to understand the enlisted and be in a position to actually do something about it. Turn your focus that way.

Just my .02

My advice is “don’t do it.” It looks like you recently commissioned. Give your new status a chance. Complete BOLC and any other branch or MOS training. Then work as an officer for at least two years. If you still hate being an officer, then look into resigning your commission. This kind of apprehension is normal with any new job.

Short answer is yes, you can resign and re-enlist. You have some baggage to work around first. Since you completed ROTC Advanced Camp, you did accrue a military obligation. 4 and 4 as non scholarship, less you enlisted time. Did you drill during ROTC or were you SMP? Good news is that you should be able to handle all of this in house with the National Guard, but they may be more receptive if you resign to re-enlist.
Remember that this all need to start with your Commander, If he/she isn't on your side, things just got harder.

Here are the steps. https://work.chron.com/request-resign-national-guard-officer-commission-25082.html

I Wonder IF This Would Be The BEST Way To Start,
Walk Into Your CO's Office, Stand At Attention In Front Of His Desk,
Render Him A Great Salute, Then Just Smile And Say
"Bye ~ Bye",
"I'm Out-a Here".