How to delete Assignee from drop-down menu?

I have already removed the Member from Organisation, and removed from Team Member list 3 years ago. But for 3 years, every time I create a new task the Assignee still appears! How do I remove the assignee who isn’t even in our organisation anymore?

hi @Lawrence_Ku, welcome to the Forum!

Please find more details and all the steps in this recent thread:

I hope this helps!