troubles with assigning a value to a list

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C#

Hi everybody. I have such interface:

public interface IChannel
    {
        string Tag { get; }
        float Value { get; set; }
    }

and in my class I create a list like :

List<IChannel> channels = new List<IChannel>();

Then I fill a list with values and finally I want to change the value in the list. I do it this way:

channels.ForEach(x=>
                   {
                       if (x.Tag == "LASV")
                           x.Value = a;
                   });

but the value of an element with tag "LASV" doesn't changes. Any ideas why?