In the final section of the DPRK missile base, Fisher has 3 minutes to stop the missile. From where the missile launches, head right and down into the door to the command center. The abort codes are on the PC to the right of that door. The codes must then be entered in one of the missile command center's PCs, which are the two rooms near the large elevator (lift) leading to the base commander's office on the level above. Assuming you took out all the enemies in that area, the three minutes are more than enough time to abort the missile.