how to access 3rd element in the list c# code example

Example: get both item and index in c#

// add this to your namespace
public static IEnumerable<(T item, int index)> WithIndex<T>(this IEnumerable<T> source)
{
    return source.Select((item, index) => (item, index));
}

//do something like this

foreach (var (item, index) in collection.WithIndex())
{
    DoSomething(item, index);
}