CSOM Update and add using c#

Question

i am trying to add items from one list to another list and able to add the items but how should i modify my code so if item exist in destination list update the item else create new entry ?

I have modified my code and trying below query but not getting expected results is this right way ?

below is my code for add item ?

Done more updates in code which i am trying ..

static void Main(string[] args)
        {
            string userName = "";
            Console.WriteLine("Enter Your Password Please  ------- ");
            SecureString password = GetPasswordOfYourSite();
            ClientContext contextSource = new ClientContext("SourceSite");
            contextSource.Credentials = new SharePointOnlineCredentials(userName, password);

            List sourceList = contextSource.Web.Lists.GetByTitle("ListA");
            
            CamlQuery query = new CamlQuery();
            CamlQuery cq = CamlQuery.CreateAllItemsQuery(200);
            ListItemCollection source = sourceList.GetItems(cq);
            contextSource.Load(source);
            contextSource.ExecuteQuery();
            using (var clientContext = new
            ClientContext("DestinationSite"))
            {

                List lst = clientContext.Web.Lists.GetByTitle("ListB");
                ListItemCreationInformation itemCreateInfo = new ListItemCreationInformation();
                CamlQuery query2 = new CamlQuery();
                foreach (ListItem SourcelistItem in source)
                 {
                    query2.ViewXml= "<View><Query><Where><Eq><FieldRef Name='Title' /><Value Type='Text'>" + SourcelistItem["Title"] + "</Value></Eq></Where></Query></View>";
                    ListItemCollection lic = lst.GetItems(query2);
                    clientContext.Load(lic);
                    clientContext.ExecuteQuery();

                      try
                        {
                            if (lic.Count <= 0)
                            {

                                var employee = contextSource.Web.EnsureUser(((FieldUserValue)SourcelistItem["Account"]).LookupValue);
                                var supervisor = contextSource.Web.EnsureUser(((FieldUserValue)SourcelistItem["MGR"]).LookupValue);

                            contextSource.Load(supervisor, user => user.Id);

                            contextSource.Load(employee, user => user.Id);
                            contextSource.ExecuteQuery();
                                ListItem DestnewItem = lst.AddItem(itemCreateInfo);
                                DestnewItem["Title"] = SourcelistItem["Title"];
                                DestnewItem["Account"] = new FieldUserValue { LookupId = employee.Id };

                                DestnewItem["MGR"] = new FieldUserValue { LookupId = supervisor.Id };
                                DestnewItem["Country"] = SourcelistItem["Country"];
                               
                                DestnewItem.Update();
                            }
                            else
                            {
                               // UpdateList();

                            }
                        }

                        catch (Exception ex)
                        {
                            Console.WriteLine(ex.ToString());

                        }

                    }
                contextSource.ExecuteQuery();

                }
            

        }