To train characters, you need XP and the shooting range. The shooting range is located on the left of your district. Your shooting range functions as your training ground. You can level up your characters by upgrading the shooting range and battling to gain XP. From level 10 on, you will need ammunition (ammo) in addition to XP and the shooting range. When you have enough XP you will be able to train your character. You can see which character you are able to train by clicking on the character overview and clicking on the character with the pulsing arrow. Click on the character and then on the “train” button to level-up your character.
If your character needs to be healed, training them will automatically also heal the character. When your character has finished training, you can see a blue pulsing circle over the character in the character overview.