I want an intra-post transfer. How can I accomplish that?

You're getting a lot of advice here that may seem contradictory at first so let me explain the overarching picture so that it all ties together, and I will explain why I recommend against chasing the IPT down the rabbit hole.

Every transfer requires the approval of the higher command. There needs to be a reason, and the approval of higher. If you want to transfer companies, the battalion must approve. To transfer battalions, the brigade must approve. Brigades, the Division approves. Divisions, the Corps approves. I don't think there are any posts with two separate Corps, so that is moot. If you want to transfer MACOM, HRC must approve. That is your branch manager. When you are looking at a unit to transfer on post, it matters what your highest shared command is. No matter what anyone tells you, what letters of acceptance or release you may have, only your branch manager can move you from one MACOM to another, even if it's two blocks down the street. Those assignment instructions must come from HRC, and anyone who promises to move you without the branch manager to another battalion in another MACOM is blissfully unaware or flat out lying.

Second part is the reason. Why are they asking to move you? If you want to move companies, your 1SG has to get with the other 1SG within the battalion and the battalion moves you. Lets say you want to move to a different battalion within the same division. Your CSM talks to the BDE CSM who talks to the BDE CSM in the other brigade. The division approves the move. But why should he move you? What is the justification to move you? Sometimes when people are in their reenlistment window a CSM will offer to move someone who wants to move but stay on post. That's a drug deal they ware willing to make. If you want to switch MACOM's, go to a BCT in a FORSCOM unit, or a SF Group assignment, or work at a hospital, or an AMEDD assignment, HRC has to approve the move. They have time on station rules that can only be broken with an exception to policy. Exceptions are for exceptional cases. Unless you are getting a compassionate move because you need to take care of your dying wife, or you are the victim of a sexual assault from someone within your unit, your case is not exceptional enough for HRC to break its time on station rules.
While you can approach your CSM to move, you need to picture how that conversation will go. Why do you want to go? Your career progression? Well, they will have a serious conversation about how you can be learning your job, the Army, leadership, and progressing your career in your current station. Is it because you are exceptional? Why would they want to trade you away then? You're asking a CSM to trade away a known value for an unknown value. They don't know what type of person the other unit will give away. No unit wants to give away a good Soldier. Plus they have to find another Soldier from the unit you want to go to, same rank, who wants to go where you are.

What usually happens in these IPT's is that the Soldier approaches the 1SG or CSM about the request. They tell the SM they will look into it. It turns out to be a lot more work than it's worth, or they don't get an answer in a timely manner. Months go by and one of the two SM is still waiting on a letter of release from some general, or it just got put on the back burner, or no one volunteers to move. Now, the Soldier has wasted months of valuable time and is more disillusioned because they feel the leadership led them on and failed to come through for them.

So, can you ITP? Absolutely. Will you? In most likelihood, in your situation, you will not. Your time is better spent pursuing efforts more likely to come to fruition, or invest your time in your current location wisely by concentrating on self development until you can move.

Talk to your Div CM SGM, they may be able to help you out. But you better have your stuff together. Give them a call, have talking points, fresh haircut, uniform strac, love me book (PT, weapons, certs), and know where you'd like to go. Ensure you have permission to go.

There are two things you can do, you can contact your branch manager to see if there are any available slots on your current installation for your grade. The second option is you can inquire from other organizations on the installation to see if they are in need of and have any slots for your MOS. If they do you will have to schedule an appointment with that Battalion CSM to talk with him about getting a letter of acceptance from him/her to be assigned to their unit. If they do this, you would have to get a letter of release from your current Battalion, which mean you would have to talk with your CSM as well. Both Battalions would have to be in agreement with the transfer. The draw back to this is, some Battalions won’t do a leeteyof release unless they can get another Soldier from the Battalion that’s accepting you. However, it won’t hurt to try this approach especially if you’re trying to stay at your current installation. Good luck to you...