Customizing drop-down menu for sequence questions

Hi! I'm creating a sequence drop-down question. It has six drop-down boxes. How do I make each selected option disappear in the drop-down menu?
eg) When I select "1", I don't want it to appear in the drop-down menu. I only want unselected options to appear in the drop-down menu.

I'm using this question type because I need it to be fully accessible.

Thanks!