The details of jpg photos list 24 bit. How do I set the supposed default of 8 bit depth in JPG?

On the edit screen, the photo is listed as rgb/8 in jpg. In checking the properties of jpg photos, the bit is listed as 24. I need to have 8 bit, which is the supposed default for jpg. How do I set for 8 bit? (Or is the 24 bit in properties referring to something else?)