If it is possible to safely pull the garage door manually to a closed position before attempting any repair do so.
Manual garage door stuck closed.
You can view this video on how to safely open your garage door with no power here.
When attempting to fix a garage door that is stuck open make sure to turn the garage door opener off.
Once the lever is disengaged you should be able to open.
However if you encounter resistance stop.
Locate the emergency cord on the overhead track of your garage door opener.
How to close your garage door by hand 1.
Some garage doors have a full lock system which enables you or anybody to lock your garage door from the outside by only turning the handle.
Garage door locked surprisingly your garage door just being locked can be causing your problem.
I managed to get a camera inside to look upward and can see that one of the cables that attaches to one of the spring latches has broken.
Advice guidance steps to follow and information on what to do when your manual garage door will not open the one thing that can be virtually guaranteed in life is that if something is going to go wrong it will occur at the time you least need it to happen.