- Go to "Settings".
- Scroll down to the bottom and tap "About phone" or "About tablet",
- Scroll down to the bottom of the "About phone" and locate the "Build Number" field.
- Tap the Build number field seven times to enable Developer Options. Tap
seven times and you'll see a countdown that reads "You are now 3 steps away from being a developer."
- When you are done, you'll see the message "You are now a developer!".
- Tap the Back button and you'll see the Developer options menu under System on your Settings screen.
Now, you can enable USB Debugging mode.
- Go to Settings>Developer Options>USB Debugging. Tap the USB Debugging checkbox.
Sauce: https://www.kingoapp.com/root-tutorials/how-to-enable-usb-debugging-mode-on-android.htm