how can i make a garage door opener run in one direction only
The problem is that all garage door controllers built since roughly 1990 automatically stop , then reverse direction when you hit the control button.  (Yes, I used to have a 1986-era opener where you could stop the door with the button but not reverse it. )

Since the control logic, aside from limit switches and strain sensors, is almost certainly hardwired into the control electronics board, you are going to have some difficulty.

What I'd do is remove the electric motor entirely from the electronics. Make sure you know what voltage drives the motor, and wire an appropriate supply directly to the motor (with on/off switch, of course).