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.