Help with blotchy colour cast background

First of all, get the exposure and white balance right. This should be done before bringing the image into Photoshop. Shoot raw files in the camera, give it enough exposure, and set the white balance with the eyedropper in ACR (Camera Raw). The first is the original, the second how it should look when you open the image into Photoshop:

You can see that your lighting is uneven here, perhaps mixing a central spot with daylight. Ideally, this should also be taken care of before you press the shutter, not after. But if this is what you have to work with, the best way to fix it is with masked adjustment layers. Set up an adjustment to correct it, invert the mask so that it's black and thereby hiding the adjustment. Use a soft large brush to paint in the adjustment gradually, until you're satisfied.

Any blotching beyond all this is probably the result of jpeg compression. Jpeg compression is extremely destructive, avoid it until the very end (or preferably avoid it altogether).

and here:

https://www.slrlounge.com/how-to-easily-correct-red-blotchy-skin-in-photoshop/

Hi, please take a look here:

https://helpx.adobe.com/it/photoshop/how-to/remove-unwanted-color-cast.html