I find it hard to answer "how would you do it differently" after the biggest achievement question as obviously I have prepared my biggest achievement question as an “achievement” and thus I got stuck.
the idea is to show that "perfection" does not exist and that you are humble to show and acknowledge that there are always ways to improve and to do "better". It could be around the timeline, the people management, the planning, sometimes it could be even putting yourself first, communication, etc.