Eternity protector king

How can i change my mos? - how to do a da 4187

I went into the army of the 31B and 3 weeks prior to the end of AIT and MOS hated my class and I want to go to a mechanic. Who knows how I do this? I've heard that I may be a complete DA Form 4187, and the use of the mark but I am not sure I am in the army, new, if he asked me to use. If anyone any advice on how I can go back to school needs, I would be very happy. (Who knows the loop holes or ways around the rules of the army, it would also) welcome