You are probably already doing this but push up on the bottom of the door while pulling on the top to get the `roller' back into the track. However, my door has a glide that is rectangular in shape so if it gets sideways out of the track it will be almost impossible to get it aligned. You should be able to see what kind of `roller' by looking at the one you can see.
I would try disconnecting the close roller which would drop down the door which might allow it to be pulled out.
We reinforced the track that we could get to with extra screws and always travel with the door in the closed position.
Dick_B
2003 SunnyBrook 27FKS
2011 3/4 T Chevrolet Suburban
Equal-i-zer Hitch
One wife, two electric bikes (both Currie Tech Path+ models)