As per this article : macOS Sierra: Use global keyboard shortcuts
Keyboard shortcuts let you quickly perform tasks by pressing keys on your keyboard. For a list of macOS keyboard shortcuts, see the Apple Support article Mac keyboard shortcuts.
You can disable or change many of the “global” keyboard shortcuts, which are shortcuts that work the same in most apps (for example, taking a picture of the screen by pressing Command-Shift-3).
Changing or disabling a shortcut may be useful if, for example, one of the global shortcuts is used by a specific app for a different purpose. In this case, you can either disable the shortcut that you don’t need, or assign it a different key combination.
Note: You can create keyboard shortcuts only for existing menu commands. You cannot define keyboard shortcuts for general purpose tasks such as opening an app or switching between apps.
- Choose Apple menu > System Preferences, click Keyboard, then click Shortcuts.
- Select an item in the left pane then, in the right pane, select the checkbox beside the shortcut that you want to change.
- Double-click the current key combination, then press the new key combination you want to use.You cannot use each type of key (for example, a letter key) more than once in a key combination.
- Quit and restart any apps you’re using for the new keyboard shortcut to take effect.
If you assign a keyboard shortcut that already exists for another command or another app, your new shortcut won’t work. Find the menu command that’s using it, then reassign the keyboard shortcut for that item.
To disable a shortcut, deselect the checkbox next to its description in the list.
If you want to return all the shortcuts to their original key combinations, click Restore Defaults.
And an another article : macOS Sierra: If a keyboard shortcut doesn’t work
It’s possible to have keyboard shortcuts for one app that conflict with another app. For example, Command-Space bar opens the Spotlight menu, but in another app it might be used for switching between different input methods.
- Choose Apple menu > System Preferences, then click Keyboard.
- Click Shortcuts. A yellow warning triangle appears next to conflicting keyboard shortcuts. Click the shortcut, then change it.
