Adjusting HVAC damper
Welcome to the wide, wide world of second story air conditioning.
If this was done to prevent it from being manipulated they wouldn't have installed it. This was done just to prevent the damper from closing due to air flow. Find out where this duct feeds and if it's to the first floor try closing it a bit to divert more air to the second floor. If this does feed the second floor, you might want to add a duct fan to increase the air flow. They can be controlled manually by a switch or hooked up to your air handler. Good luck.