I would suggest using the File>Open in Camera Raw option. This will bring up the Adobe Camera Raw editor, even if your file is not a raw file. Assuming there is some detail available in the sky, you can bring it out by lowering the Highlights and Whites sliders and maybe increasing the Blacks/Shadows and Clarity. You can also try out the other sliders to see if they work for your image. Once you have completed your edits, click the Open Image button, then save the file in the normal way.
Here is a random photo with a sky lacking any detail. You can see the added definition of the clouds when making the adjustments discussed above: