If a single roller has popped just at the bottom of the track, some owners can walk it back with a pry bar and a firm hand, and there's nothing wrong with trying that on a door that isn't under spring tension at the moment. Where it stops being a DIY job is anywhere the door is still attached to a wound torsion spring - pulling a panel back into track alignment while that spring is loaded is how people lose fingers, not a scare tactic.
The other place to stop: if the track itself is bent rather than the roller just having jumped it, bending it back rarely holds. It'll walk out again within a few cycles and now you've got a weakened rail. That's a straight call, not a trial-and-error project.