Ducky One Mini 2 is a "60% keyboard" so it doesn't provide a direct way of pressing the Delete key. You should use this shortcut (Fn + Backspace) instead.
More: Display all Ducky One 2 Mini shortcuts.
For beginners: How to press
Fn + Backspace on your keyboard?
Typically you first hold down modifiers (if exist), and then press remaining key(s) in the shortcut. So,
Press and hold