C# Online Compiler | .NET Fiddle

using System;
using AutoMapper;
using System.ComponentModel;

public class Person
{
	public string FirstName { get; set; }
	public string LastName { get; set; }
	public int Age { get; set; }
	public string Address { get; set; }
	public string Email { get; set; }
	
}

public class PersonVM
{
	
	public string Name { get; set; }
	public int Age { get; set; }
	public string Address { get; set; }
	public string Email { get; set; }
	
}


public class Program
{
	public static void Main()		
	{
		
		var config = new MapperConfiguration(cfg => { 
			cfg.CreateMap<Person, PersonVM>().ForMember(dest=>dest.Name, opt => opt
														.ResolveUsing( src =>{ return src.FirstName + " " + src.LastName;})
													    
													   );
										
										 
		});
		
		IMapper mapper = config.CreateMapper();
		
				
		var person = new Person { FirstName=null , LastName = "Dev", Age=10, Email = "test@test.com", Address="Test Address" };
		
		var personVM = mapper.Map<PersonVM>(person);
		
	    Console.WriteLine("\nperson.FirstName : {0} \nperson.LastName : {1} \nperson.Age : {2} \nperson.Address : {3} \nperson.Email : {4}", person.FirstName, person.LastName, person.Age, person.Email, person.Address);
		Console.WriteLine("\npersonVM.Name : {0} \npersonVM.Age : {1} \nperson.Address : {2} \nperson.Email : {3}", personVM.Name, personVM.Age, personVM.Email, personVM.Address);
	}
}

Cached Result

Key:GB    Value:United Kingdom
Key:US    Value:United States
Key:CA    Value:Canada
Key:FR    Value:France
Key:ES    Value:Spain