They're not going to know unless you show them. If they only go into the coop to lay and sleep, they may be focused on those areas (nests and roosts) and not necessarily spend time looking around and noticing that you've moved the feed. They may very well walk past it and not even notice it's there, if they don't know to look for it (chickens aren't all that smart, contrary to chicken fans' claims). Draw their attention to it somehow. Is your coop big enough for you to walk into? (ideally it is... tiny coops are impractical for many reasons, this being one). If it is, go in there and call them over, maybe rattle some treats and put the treats in the feeder as they watch you. When they go for the treats, they'll notice that there's other food there, too. Do this a few times and they'll get the idea. They may still go to the feeder looking for treats, but when they don't find any, and they're hungry, they'll make do with the regular feed. Now, if your coop isn't big enough for you to walk into, figure out a way to still call them over to the feeder - maybe open the human access door and stand there, with your hand next to the feeder, calling them or rattling the treats, or whatever other means you have of drawing the chickens towards you.
