Use your finger to move your character.

Drag your finger up and down the screen to control your character. OR Control your character by dragging your finger up and down the screen. I do not think you need to remind them to keep their finger on the screen. But if you insist: Drag your finger up and down the screen without lifting it to control your character.

The sentence "Drag your finger up and down the screen without lifting it to control your character." from Christian Martinez is really good.

Touch and hold the character, then control it by dragging your finger up n down.

Thanks a lot!!!!! ;)