AGP J-Hook Liner sagged while filling - 1/2 full, 4 foot section slipped 4-6"

I have an above ground pool in the house I'm renting that hadn't been taken care of for years. After removing 1200 lbs (literally) of wet leaves/frogs/dead possum, and draining the pool, I began to refill it from our well. It's a 24'x48" above ground pool with surrounding 18" deck and rails. Nice pool. Liner seems to be essentially pristine. I didn't notice any part of the liner out of the hook when I drained it adn cleaned the leaves out. Everything looked essentially perfect. So the slow process of filling from our well began. In a matter of 2 1/2 days I got the water to about 22" (around 7000 gallons by my guess). While I was at work a 4' section of liner slipped out of the J-hook and sagged down about 4-6". I've tried spraying with hot tap water and stretching - while the liner did stretch I couldn't get it to reseat in the j-channel. There is a small fold in the liner on the floor below the slip, but it's only about 1". I've heard about using a plunger to "suck up" and "push" the crease over to the wall and maybe pull or float the crease upwards - perhaps giving me enough slack to reseat the liner Jchannel. What are my chances of this actually working? I'm trying desperately to avoid draining the pool again.

membership updated.

(Sorry, but AG pool repair is not in my area of expertise.)

I'm going to email Ted aka Waste who is our resident pool installer to see if he can help. He's a busy guy this time of year, so we will keep our fingers crossed that he can help!