For example you have a base class and a class that inherits it like below.
public class A
{ }
public class B : A
{ }
And you have generic list of these types. Then if you want to convert List<B> to List<A>
You can use this code block:
List<B> listB = new List<B>();
List<A> listA = listB.Cast<A>().ToList();
Happy coding.