wow, this one might be some fun! are you able to get the liner back into place?? you can lower the water a few inches and use near boiling water to pour on the liner to allow it to stretch a little bit. if you cant get the liner back into place, there is no point in SLAMing it to clean it, you are going to have to replace the liner. looks to me like you should be able to get it back into place with some muscle. after that....its going to be a LOT of bleach and a lot of scooping out gunk from the pool. first thing, see if you can get that liner back into place. and welcome to TFP!
if you can get the liner in place, that pool will be sparkling clear in a few weeks, we have seen much worse here!