Shop vac the sand out of the tracks. Now the hard part-undo the liner where you are working making sure to clip it GOOD so it can't all walk out on either side. Sweet talk wife into getting between the liner and wall inside the pool. She will need to use her feet to GENTLY nudge/push/kick the wall back into place. YOU on the outside might need to nudge/push/kick the bottom rail to help the wall get back in the track.
You might even have to wiggle the wall some to get it to move a bit.
You might even have to wiggle the wall some to get it to move a bit.