Replace array.convertall in netcore 1.0

This is an extremely basic task what you are asking to do. I think you need to read more programming tutorials/C# tutorials to full understand what it is you are trying to do.

An extremely basic idea of what you can do:

public class American
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }

    public class European
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }

    var a = new American();
    a.Name = "Name 1";
    a.Age = 44;

    var americans = new List<American>();
    americans.Add(a);

    var europeans = new List<European>();

    foreach (var american in americans)
    {
        var convert = new European();
        convert.Name = american.Name;
        convert.Age = american.Age;
        europeans.Add(convert);
    }

    //europeans contains your converted americans

There are automappers and what not, but given you were asking to do something as basic as this, I am afraid automappers might be too confusing at this time. You should work on the basics before jumping to more complicated libraries.