Need Help reverting to stock firmware! Netgear EX3700

Hello all, I have played around with OpenWRT on my Netgear EX3700 and decided that I would like to go back to stock firmware. I have played around with the settings a small bit but it will not let me upload my stock firmware file. The stock firmware file from the Netgear page is a .chk file, but OpenWRT will not let me flash it. I have tried using TFTP when booting up the wireless extender, but no luck. I am not good a linux or anything, but I do have good knowledge with computers. Is there anyway I can revert to stock firmware? I have read the wiki and stuff but it does not make any sense to me. If someone could help, it would be greatly appreciated. Thanks!