On the 2nd Floor of Tower of Insolence, you should find a door that is red. If you stand right next to the door and face it, the summon your mount it should make your mount on the other side of the door. You should be able to mount your mount if you did it correctly. BEHIND THIS DOOR ARE RAID BOSSES AND RAID FIGHTERS. Becareful with this or you’ll die quick.
Oh I forgot one thing, once you do get inside there is no leaving that room. Since the door doesn’t open.