If I remember correctly, you shoot in raw, right? One of the main advantages of shooting raw is being able to correct the white balance in post nondestructively (no loss of image quality). This is done during the raw conversion with the temperature and tint sliders. First slide the temperature slider to the right until the image becomes very obviously too red. Then slide it to the left until the image becomes very obviously too blue. Then slide it back to the right (but not as far as before) until the image becomes a little too red. Then slide it back to the left (but not as far as before) until the image becomes a little too blue. Keep moving the slider back and forth in increasingly narrower increments until you end up at a neutral point between red and blue. Then move down to the tint slider and repeat the same process, but this time you'll be finding the neutral point between magenta and green. Next I recommend going back and rechecking the temperature slider and going back and forth between the two sliders a few more times, since changing one can sometimes alter your perception of where the neutral point is on the other one. In the end, you should end up with an image with a neutral color balance without any color casts.
If you want to perform color correction on non-raw images, then you can do that by adding a color balance adjustment layer to your image in Photoshop. I recommend only adjusting the midtones and using the preserve luminosity option. The process is very similar to what I described above, but there are three sliders instead of two. You just try to find the neutral point on each slider, and you cycle through them several times until you cannot make any further improvements.
Color correction by eye like this is a skill that takes some practice to develop more so than just following the instructions on how to do the technique. The hardest part is to train your eyes to recognize the difference between small color casts and neutral color balance. Our brains are very good at automatically compensating for color casts. It's what allows us to determine the color of objects under light sources of very different color temperatures. But that can be overcome with some patience and practice.
NANFA Youtube Channel 
