how to eliminate yellow cast in Photos

open the photo in the editor in Photos. Then use the white balance compensation tool in the adjustmentpanal.. It has two tools - a slider to make the lighting colder or warmer (shift the color towards blue or yellow), or the eye picker. Sample a color in the image that should be grey instead og yellow and photos will adjust the lighting.

If there are people in the picture it may work better to sample the skin tools instead of white or grey, with the sampler set to "skin tones".

If you can easily change the white balance in your camera you may want to correct the white balance in the camera before you take the picture. Or use the flash. On my iPhone X the flash light has a color perfect for keeping the skin tones right.