Belltann,  uou can 5ake the champion out of the pit by going to your tavern, selecting another champion thats ready to rank up, you can then select the champion that's stuck in the pit, by clicking on the relevant tick. You can confirm that you want to remove it from the pit, once you confirm you can cancel the rank up of your champion. Your stuck champion is now free and you can select a new one in the pit. Not an ideal fix but it is a work around.