As far as I know its not possible to swap your dual and main classes. I think your only option would be to change your healer dual class to something that doesn't conflict with your main in the subclass system and then change your main class to healer. After this was done your main class would still be lvl 86 (now a Healer instead of Othell) but your dual class would be reset to lvl 85 by the dual class change process. I think that is your only option to make your main class a healer.