Yup, the comments by TheBestCPU (John) are right on the mark, particularly, his cautions about using automated methods to do white balancing.
Let me add one thing to his comments. Often, while there may not be anything in the image that you know for sure is a neutral gray, there may be areas in the image that do have well known colors -- just not grays.
So if you can make these come out the right color (instead of working with grays), you often can get a very acceptable color balance, quite similar to what one would get had a gray area been present and used. For example, a commonly occurring, reproducible color in many images is skin, particularly, if it is someone (eg, member of your family) that you have photographed previously with good success w.r.t. color balance.
The way to do this is to use a "Curves" adjustment layer. Read off the RGB values of the skin in the image that needs to be corrected (TBC), as well as the RGB values of the skin in your reference skin image, and enter Red_TBC on the x-axis of the red curve, and Red_goal on the y-axis of the red curve, then do the same for the Green and Blue curves.
Here are some web pages that describe this technique:
http://www.zuberphotographics.com/co...rves-color.htm (scroll about 1/3 rd of the way down the page to the section titled, "Color Channels Technique")
http://www.zuberphotographics.com/co...hop/curves.htm (probably too basic for you).
And here is a post I wrote in this forum where the goal was to adjust a recently acquired photo of a tooth to make it have the same color as a reference (ie, goal) tooth:
https://www.photoshopgurus.com/foru...r-analysis-post1533709929.html#post1533709929
If you have any questions, don't hesitate to ask.
Cheers,
Tom M