Highly confused on how to order by objects inside an object

[sapator]

This confuses me.

I have this code:

Private Sub SurroundingSub()
    Dim schcls As Schedule = New Schedule()
    schcls.Screens = schm.Screens
    Dim foundDocuments As List(Of ScheduleScreen) = schcls.Screens.OrderBy(Function(o) o.ScreenNumber).ToList()

    For Each sr As ScheduleScreen In schcls.Screens
     sr.Sessions.OrderBy((Function(o) o.SessionStartString).ToList()
    Next
End Sub

Of course this will not work as it's immutable but you get the idea.

The result must be and order by on SessionStartString ( that is Ulong date representation such as 20230907170000

Is there an automatic way? Should I create a new list and start adding? Then again how would I add sorted results with Linq? Or do I need some comparisons?

Thanks.