Currently, the troop that is displayed as a players favored troop is set automatically. However, most of the time, that troop is not the players actual favored troop or is no longer that troop that is displayed. I think you should be able to manually change what troop is displayed as your favored troop.
It should display automatically at first before the player has chosen one, yes, but when you go to your profile i think you should be able to click on your favored troop and a list of all troops that the player owns will pop up, there should be a filter like in the normal troops tab, then you should be able to select your actual favored troop. This would be more of a quality of life change than anything, it wouldn’t disrupt any of the game core mechanics and overall would just be cool to be able to change.