I was focusing the camera using the ground glass, and I extended the sliding track past the end of the bed. Now I can't get the track to move back into the camera body. I think I did this once before, but I can't remember how I resolved the issue the last time. Can anyone help?

I assume you're using a Pacemaker or Anniversary Speed.
If the bed was 90° to the body and you ran then out to where the focus shaft no longer engages the rails then simply push in toward the body on the center of the rails while turning the focus knob rearward until the gears mesh.
If the bed was dropped then run the rails inward with the bed dropped until the rail link is just past the rear edge of the bed then align the rear section of the rails with the bed guides then turn the focus knob forward until the rear section of the rails is fully on the bed then return the bed to the 90° to the body position then turn the focus knob rearward until the rails are fully into the body.
If the bed is at the 90° position with the rails fully on the bed then shims are missing from the body guides, too many/too thick shims are under the body guides or the bed hinge is bent. Align the rear of the rails with the slots in the body guides then run the rails in by turning the focus knob rearward.

Thanks for the response. You're correct, I'm using a Pacemaker. I discovered that the track inside the camera body was dirty, and once I cleaned it a bit the rail slid right in.