Make sure you have the latest version of GoodLock. I believe it's 2.2.04.75. Once you've done that open the app and switch to the Life Up tab. From there scroll down and find the Sound Assistant app. You'll need to tap on the download button to download and install it if you haven't already. Once installed, launch Sound Assistant. Tap on Customise volume panel and on the bottom of the next screen you'll find a Custom button. Tap on that to find the Standard Panel options. Ensure that the Show volume level button is enabled if you want to see the volume percentage.
You can also access the Expanded panel options by changing to the tab at the bottom.
Hope this helps.