Stop operating the door
An off-track garage door can become unstable. A roller may have left its track because of impact, cable problems, track damage, worn hardware, or uneven movement elsewhere in the system.
Do not force it back into place
Continuing to run the opener can twist panels, damage tracks, pull cables, or cause the door to shift unexpectedly. Leave the door in place and arrange inspection.
What repair may involve
The cause should be addressed, not just the displaced roller. That can mean checking tracks, rollers, cables, drums, brackets, hinges, and spring balance. See cable, roller and track repair.