E_l, did you have someone install the liner for you? If so, any liner tucks should be their problem to fix (unless your pool is older and they won't come back to do it). What the others have posted here is fine advice, however be careful! IT IS POSSIBLE TO POKE YOUR FINGER THROUGH A HEATED LINER!! If it won't go easy with some heat, STOP! There are tricks/ techniques that can get the liner back into it's bead, if you need them simply ask (I couldn't possibly type them out in the space of a reasonably short post), and we'll get together and I'll fill you in on what and how to do it. While I'm at it, water from the kitchen sink is fine but even a hair dryer can burn a hole through the liner - have patience and don't wreck the liner, there are few 'tucks' I've 'needed' the hot water or hair drier for, and that's only been because the air temp was < 60 or the liner was ~ 10 yrs old, however, I frequently use both when it makes the job easier.
One method of heating the liner that hasn't been mentioned (probably because I'm the only one I know who uses it) is to rapidly rub a rag across the area in question, ie generate friction, no need to run an extention cord or haul a bucket from the kitchen
I just want to make sure you don't damage the liner. - Waste