How to insert and remove all elements from dropdown list - ASP.NET

 For Insert

ddlDiscipline.Items.Insert(0, new ListItem("--Select--", "--Select--"));

For Remove:-

ddlDiscipline.Items.Clear();

 ddlDiscipline.Items.Insert(0, new ListItem("--Select--", "--Select--"));

reference:- https://meeraacademy.com/how-to-use-clear-remove-and-removeat-in-dropdownlist-in-asp-net/