How to open a Henderson single panel door from the outside?

Does anyone know how to open a Henderson garage door from the outside? The locking mechanism is still working fine but when my wife closed the door last she heard a "funny noise" but closed it anyway...

Now the garage door wont open. It seems to be just the left hand side of the door that isnt budging, the right side seems free to move as you can still get a little movement there.

I was just going to force it and claim it on my insurance but thought i'd ask you folks on tinternet first.

any and all ideas welcome.

Thanks in advance.