Ok, so I have 4 players in total, 2 are leveling but would like to get some xp on the level ones.  How do I switch my team?  When I go to the player page I can unlock them, but can’t choose them in a mission.  Thanks for any help!

If I understand correctly, it sounds like you have two of your champions training in the sparring pit, but want to also use them in missions? If this is the case, you can have a champion training in the sparring pit, or available for putting on a team, but not both at the same time. If you want to make your champion available for your team again, go to the sparring pit, tap on the hero, then in the "select champion" screen, deselect the champion and press confirm, they will then be removed from training and will be available again for your team.