use linq to get data from different list to different list c# code example
Example 1: select from list where not in other list c#
var result = peopleList2.Where(p => peopleList1.All(p2 => p2.ID != p.ID));
Example 2: select from list where not in other list c#
var result = peopleList2.Where(p => !peopleList1.Any(p2 => p2.ID == p.ID));