I attempted to make apple cider, buying Kirkland apple juice (6 Gallons) and 500g dextrose. All i did was pour in the juice and pitched the yeast (s04) ontop of the juice at about 20deg Celsius, O.G reading of 1056. The fermentation kicked off strong, bubbling and dropping gravity to 1034, here it has stopped on day 4 for the last 4 days. The wort did drop to 17deg celsius but aparrently this is within its temperature range? I have since raised the temp to 20-22 steady, and nothing... Should I pitch another packet of yeast? Is there any saving the cider?
4 days of fermentation is a very short amount of time for a cider. Let it go. Add yeast nutrient if you can acquire it, ideally something with both general yeast nutrients (yeast hulls, vitamin B) and DAP. Cider does not really have all the things yeast wants to be healthy, and needs additional nutrients. Look in to "staggered nutrient addition" if you want a better protocol for the future; also, look in to sulfiting.
That being said: did the Kirkland apple juice already contain preservatives such as potassium metabisulfite or any other yeast-unfriendly compounds? Hopefully not.
If not, and in any case, give the cider at least 2-3 months of ferment and conditioning.
The S04 yeast strain is notorious for dropping out with a temp drop. You have warmed it back up which is good. Now you need to rouse the yeast back into suspension. Either through some shaking or gently stirring if you can get a long enough implement into your fermentor. A little yeast nutrient/energizer would help too.