My first step was to take the sky and turn it into it's own layer, I used the magic wand feature to create the selection. The first attempt was to take the bison out of the picture, that did not go well and I had to focus on getting the sky out of the picture. The bison fur was too difficult and time consuming to try to use the layer mask on.
Then I lowered the brightness and increased the blue in it.
After that I removed some rocks out of the snow and used fill with content aware
Then I smudged the clouds to make the sun bigger and also add bison horns to the sun and a cloud
Although after I smudged the clouds it stood out too much so I had to use the stamp tool and make it kind of see through to add some more natural cloud colors to the bison heads
Overall I like the darkness of the sky, and the line that was between the bison and sky I smudged to blend in