Yes warm/hot water can work but it depends how much warp you have. You may need to use two or three attempts to get it back to shape. Submerge it for 2 or 3 minutes then see how much you can move it, if is is thick styrene it may need more like 5 minutes so its best to try this way first. When you can get it to move with a little pressure try a dry fit and clamp it in place. Dont over stress it, white lines can be a give away for this in the styrene. It may take two or three attempts to get it to fit right so less is more in this situation take your time and dont get it too hot.
Thats how I've done it but someone may know a better way
Pmitch