If Malwarebytes for Android stops working when you try to enable Device Administrator, this is the result of a crash. Malwarebytes for Android can crash when using the Dashboard or the Settings to enable Device Administrator.
Use your device's settings to enable Malwarebytes for Android as a Device Administrator.
Android device settings vary depending on the device's manufacturer, model, or operating system. For more information about your device's settings, refer to your device manual.