How to come back to customized way d600
I'm going to assume that you did not save the settings. Here is how I set up the U1/2 modes. With the camera in S mode I set auto ISO, AF On using the AF/AE button, and Easy Exposure Compensation. Then in the 'Setup Menu' I 'Save User Settings' to U1. Then I set the camera to 'A' mode, and in the 'Setup Menu' I save to U2. I usually shoot in M mode with no auto settings other than auto focus, so when I need the camera to respond quickly I can select either Shutter Priority with U1, or Aperture Priority with U2.
You do not need to be in one of the U modes to set it up.