How do you end Good ol boy club?

You don't. You can't stop people from having friends.

That being said, if you can show a bona fide case of discrimination then you can bring that up the chain.

But before ANY of that, maybe just sit down with your first line and let him/her know that you feel like you are on the outside looking in and would like to be a full member of the team.

Not a whole lot you can do, especially IF you're the outsider. I had a similar situation with the group I joined in Iraq. The unit had come from Arkansas and I was from South Carolina. I could do no right, in their eyes. I even had a Specialist that was friends with the Sergeant Major, probably in more ways than one. She asked me to do certain jobs, that she probably wouldn’t give to others or do herself, because she informed me, she was passing information from the Sergeant Major...I knew better. I lived thru it and parted ways after we got back...have not spoken or seen any of them since.

Look, most Guard and Reserve have a different type of relationship based on the nature of their service. While I do not ascribe to the GOBC, as long as it is not impacting the units readiness posture and relationships are not being abused professionally then just ignore it. If it is rampant and effecting the organization, speak to the most senior person you trust that is not in the group. Thank you for your service.

With a stick and stone

In reality, a easier said than done sometimes solution. Move people around. Promotion mainly, after they get pinned they go to another platoon. E-4 and below shouldn’t be stuck on the same task for 2 years. Riflemen become Drivers, Drivers become Machine Gunners or SAW. Anti Armor becomes RTOs or Grenadiers. Bradley Gunners become Team Leaders. Team Leaders become Senior Gunners. Senior Gunners go to Staff. Staff goes back to the line after 6 to 12 months instead of riding the POG train.
I also think to get selected for SFC, light and Mech time should be required.
This is Infantry oriented but there are different tastings for everyone.

So I should clarify I am apart of a detachment and we are deploying as a whole. Let’s say me and the few people from my detachment are group
A and group B is the GOBC. All the guys from group A notice group B has their favorites

If it's an actual case of favoritism and not just something not going your way, run it up the chain. Have you talked to your supervisor about it? It could be something that they don't even notice. Ignorance can cause a lot of issues which is why it's important to identify these issues early. You don't know what you don't know.

Define "Good ol boy Club " and what you believe is toxic in your leadership.

Talk, starting at the top end. I was in a unit deployment to a new kaserne in Germany as part of the Brigade '75 thing. Our battalion had been frozen (you had to reenlist or leave the service to get out) for years due to ongoing company sized 6 month TDY rotations before the final deployment. Upshot- lots of us had known each other and worked together for years, in many cases 3-4 years, then mass deployed to Germany. New people coming in to the unit called us "The Family" and saw us as the ultimate good old boys network. Actually, we had just worked together so close and so long we didn't have to talk about a lot of stuff. Once the problem surfaced we encouraged the f'nuggies to TALK to us, and TALK, and TALK some more. We did not mean to shut them out, sometimes it just happens.

So...., TALK to them.

GOBC exists to some degree in every Guard and Reserve formation, partly because MDAYs/TPUs can stay in the same organization for far too long.
If the GOBC causes a problem that is a legitimate EO issue, or violates any established regulation or policy, then you address it through the chain of command, and if that is ineffective, you take that complaint to EO or IG as applicable.
If the only problem is that the GOBC is annoying, find a different unit where the GOBC is less annoying.

Really hard, I saw a USAR unit where the Commander and 1/2 the unit worked together in his business stateside. Caused many problems