Update the values in a list

I have this code, I need to update the values in case I can not find it.

List<Rollos> set = new List<Rollos>();

Rollos temp = new Rollos();

foreach (Rollos  y in l)
{
    if (set.Any(x => x.item == y.item))
    {

        temp = set.Where(x => x.item == y.item).Single();
        if (temp != null)
        {
           // set.Where(x => x.item == y.item);

        }
    }

    else {

        set.Add(y);

    }

}