For your buddy I think it might be too late, he may not have enough time, but he can try.
A Soldier in the National Guard needs to go through his chain of command which would notify the training or readiness NCO at his or her (yes, female Soldiers can attend) unit, that person will know how to look up the school on ATRRS and get the ball rolling. Our school code is 1029. These are the class dates
https://atrrs.army.mil/atrrscc/cours...ARKSMAN&phase=
I don’t know what the procedure is for the active duty side.