Look in the bottom right side of the case if you are facing the open side, you should be able to find a small 3 cable plug (picture) that you can connect to. It may be tucked behind something to keep it out of the way, so look hard. If you can not find a connection, you can also connect your fan to any of the fan headers on the motherboard, just make sure the cable has enough slack to comfortably unplug it from the motherboard when you remove the side panel in the future... you don't want to forget about it and rip the plug off the motherboard.
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