C# Online Compiler | .NET Fiddle

using System;
	using System.Collections.Generic;

using System.Linq;				
public class Program
{ 
	public class FindPersonResultsViewModel
   {
      public int PersonID { get; set; }
      public bool ExistInContactManager { get; set; }
      public bool ActionType { get; set; }
   }

   public class PersonViewModel
   {
      public int PersonID { get; set; }
   }
	public static void Main()
	{
         var findPersonResultsViewModel = new List<FindPersonResultsViewModel>()
                                          { new FindPersonResultsViewModel { PersonID = 2, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 3, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 4, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 5, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 6, ActionType = false, ExistInContactManager = false },
                                          };



         var personModel = new List<PersonViewModel>()
                           { new PersonViewModel { PersonID = 2 },
                              new PersonViewModel { PersonID = 6 },
                              new PersonViewModel { PersonID = 8 },
                              new PersonViewModel { PersonID = 9 },
                              new PersonViewModel { PersonID = 12 },
                              new PersonViewModel { PersonID = 22 },
                              new PersonViewModel { PersonID = 32 },
                              new PersonViewModel { PersonID = 42 },
                           };

         var query =
            from pr in findPersonResultsViewModel
            join p in personModel on pr.PersonID equals p.PersonID
            select pr;

         foreach (var item in query)
         {
            item.ActionType = true;
            item.ExistInContactManager = true;
         }

         foreach (var item in findPersonResultsViewModel)
         {
            Console.WriteLine("PersonID : " +  item.PersonID + ", ActionType :" + item.ActionType + ", ExistInContactManager :" + item.ExistInContactManager);
         }
	}
}

 
using System;
    using System.Collections.Generic;
​
using System.Linq;              
public class Program
{ 
    public class FindPersonResultsViewModel
   {
      public int PersonID { get; set; }
      public bool ExistInContactManager { get; set; }
      public bool ActionType { get; set; }
   }
​
   public class PersonViewModel
   {
      public int PersonID { get; set; }
   }
    public static void Main()
    {
         var findPersonResultsViewModel = new List<FindPersonResultsViewModel>()
                                          { new FindPersonResultsViewModel { PersonID = 2, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 3, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 4, ActionType = false, ExistInContactManager = false },
                                             new FindPersonResultsViewModel { PersonID = 5, ActionType = false, ExistInContactManager = false },

Cached Result

PersonID : 2, ActionType :True, ExistInContactManager :True
PersonID : 3, ActionType :False, ExistInContactManager :False
PersonID : 4, ActionType :False, ExistInContactManager :False
PersonID : 5, ActionType :False, ExistInContactManager :False
PersonID : 6, ActionType :True, ExistInContactManager :True