Q: Change it back to what?
RGB is the default – RGB is a standard color model, displayed on your devices.
To change to other Color Mode, for example, CMYK, etc. you must 1. Image>Mode...select CMYK, etc. 2. Save your file 3. When you Open file it will no longer be in RGB mode.
More info on color modes: https://helpx.adobe.com/photoshop/using/converting-color-modes.html
... View more