How do I make a movement range for character?

Hi everyone. So I'm making a vertical shooter for mobile and I got a problem. The character should only move in the bottom half of the screen but, it should be controllable from the upper half too. So when you're touching the bottom half, the character goes where the touch goes, and when you're touching the upper half the character should stay in the bottom half (it can go right left down but not up).

I appreciate your help <3

If touch.y is less than a value, so whatever the middle of the screen is, then have the player move towards touch but override the Y by setting player Y to a specific value.