That is your 510 connector, this is what connects the positive and negative of your atomizer to the battery. There should not be any juice in there, electricity and liquids are not a happy combination.
How long have you had the mod for, perhaps it's still under warranty? I have not repaired a mini myself, but I would imagine you need to re-solder the connections to the box, then remount the 510 connector. Was it press fitted before, or was it braised or hot glued?