You can open a garage door without power in various ways. You can use the emergency release, access the garage door opener through the wall panel, or by cutting off power to the opener and manually opening it with a pull cord.

Emergency release method
The emergency release method is usually the simplest way to open a garage door without power since all you have to do is pull a cord or lever from inside or outside of your garage. This is why this method is also known as the manual override.
In order to find your emergency release, you’ll need to locate and remove any coverings placed on top of your garage door opener motor. Once you’ve done that, you can pull on the red rope hanging down from the trolley until it detaches from its bracket.
With the trolley detached, you should be able to open your garage door manually. Keep in mind that depending on your model of garage door opener, you may need to reattach the trolley after manually closing your door.
Wall control panel method
Another way to open your garage door without power is by using an alternative source of power for your wall control panel. If you have an outlet near your wall control panel, you can use a portable battery pack or portable generator to open the garage door.
The Bottom Line
In the event of an outage, you may be able to open your garage door manually. Most garage door openers are equipped with a manual release mechanism that enables you to disengage the motor while still opening and closing the door. To locate the release, look for a cord hanging from the opener rail near the spring assembly. The end of this cord has a pull handle attached to it. To disengage the opener, grasp the pull handle and pull down.