We start with this picture.
Second is step is to add a Curves Adjustment layer.
In the curves adjustment layer we choose in this case the 'blue channel'.
How to use the curve. On the left side we have the shadows and on the right side the highlights. In the highlights we want some more yellow. To do this we drag the upper right part of the curves down. We add some more blues to the shadows by dragging the slider up. To know how the colors of the sliders react you have to study and known the color wheel.
Now we simply did some split toning in Photoshop. Of course you can also split the tones using another color channels for example the red channel.
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picture from pixabay