What is the process on going from AC to AGR as an 11B Staff Sergeant with 12 years?

There is no contract option to go strait from active to AGR. AGR is an application process and it is very competitive. There are limited positions/ranks/MOS. You must be a member of the reserve or guard to be eligible for AGR positions.

There’s an AGR page on HRC that explains the application process. First you’ll need to be off active duty; there is no guarantee you’ll be accepted or even competitive for a slot, so have a strong backup plan

Change MOS to 91B or 92Y. You'll have a higher chance of getting selected.

AGR is fairly competitive as an E6, and it can be a bit of nepotistic system. You should not base your decisions solely on getting an AGR job, because it may not happen for several years in the Guard/Reserves, if ever.

ETS with an RE Code 1 and honorable discharge, as you are clearing, go see the NG career counselor and ask for the transition paperwork. Once you are out of the Active duty books, you can start to train in the unit. Best luck to you.

Well, you also need to specify what kind of AGR? Reserve, National Guard State, or National Guard Federal?
I did that as a Major. One day I’m active duty, the next I’m AGR. 15 yrs, no break in service. A seven day old Major. Good luck, it takes a lot of planning and sponsorship to where you want to get.