C# :: Store Data In Memory After Adding Values

I serialize a XML file, and i have this values here:

public class ServiceConfig {
public List<DatabaseDescriptor> Databases { get; set; }
} public class DatabaseDescriptor {
[XmlElement("Name")]

[Code] ....

I have a form1 which is a datagrid view and get's updated like this:

dataGridView1.DataSource = xmlData.Databases;

Now i have a button: get tables, and it opens up form 2, there it's supposed to appear all the tables of the selected Database, when i click on the row i get the database name so i get all the list of Tables from

DatabaseDescriptor
where
DatabaseDescriptor.Name == name
(I get this when i select the row)

But then on the 2nd form, i also have 2 textbox so i add a new table, i add the tablename and id. the new value should appear in the datagridview of the tables, and when i close it and reopen it, it should be there. Maybe i should concatenate first the values or something, how do i do?