since the war would be well known by this point in time, the equestrian government puts out a bunch of adds for soldiers and volunteers for experiments to help win the war.
Iron Will after one of his speeches to help ponies be assertive. He finds a flier for the war. he shows up at the recruiting place to try and help Equestria. BTW he wants to join the war because he thinks his motivational speeches and his strength might help win the war. once there the ponies were a little iffy about accepting him, they never expected to see a minotaur sign up but after a bit of negotiating he convinces them.
After about a month of training, he is traine