If too much of it pulls out or it sinks too deep to get back up manually or the heat/stretch method is no longer going to work because of all of the above, you do what's called "floating the liner" - essentially you start pumping your water behind the liner, this will make it float up some, this will allow for it to lift up with ease, then you can reseat it in the bead - preferrably using some liner lock to help keep it there longer, once you have almost all of it reseated, you stick your garden hose/pump behind the liner to pump the water you had put there back into the pool and once that's done you finish with the last little piece of liner that still needs to go back on.