What do you mean? You CAN choose your character. If youre playing on your phone, go to the main menu. Do you see the little icons on the right side of the screen? The one that has a flag and has the word "party" is the one you want. Press on it and then press on "Party Setup". Once you see your 3 team members and the monsters theyre riding, you can change characters by pressing on the character's face at the bottom of the screen. Do the same if you wanna change monsters (press on the monster's face at the bottom of the screen). You can also press on the yellow "Auto Setup" button at the top of the screen if you dont want to change your characters and monsters yourself. This will also equip your team with the best gear and mini-mons that you have.