You can loop through the selected items and add them to the control.  Try
something like

   Dim varItem As Variant
   Dim strUserSel as String
   Set ctl = frm!lbMultiSelectListbox
   For Each varItem In ctl.ItemsSelected
      strUserSel =  strUserSel & ctl.ItemData(varItem)
   Next varItem
   Me.ControlName = strUserSel

You should not do it by putting multiple names in a single record.    Have a
table of classes with a one-to-many relation to the atendees.   You need a
separate record for each person so as to record test
scores/completion/attendance/etc.

You have a many-to-many relationship between the people and the sessions,
i.e. each person (employee?) can attend one or more sessions and each sessi0n
can be attended by one or more people.  A many-to-many relationship is
modelled by a third table with two foreign key columns referencing the
primary keys of the two referenced tables, so you might have tables
Employees, Sessions and Attendances, the latter with foreign key columns
EmployeeID and SessionID.  Together these two columns constitute the primary
key of the table.

Any other attributes of the employee's attendance at a particular session,
e.g. an assessment rating, would be represented by columns in the Attendances
table.

For data input you would use a form in single form view based on the
Sessions table and within it a subform based on the Attendances table.  This
would have a combo box bound to the EmployeeID column along with controls
bound to any other columns in the table, apart form the SessionID column
which you don't need to show on the subform at all.  The subform would be in
continuous form or datasheet view and linked to the parent form on the
SessionID columns by setting the LinkMasterFields and LinkChildFields
properties of the subform control (that's the control on the parent form
which houses the subform).

Assuming the Employees table has columns FirstName and LastName the
RowSource property of the combo box on the subform bound to the EmployeeID
column would be:

SELECT EmployeeID, FirstName & " " & LastName AS FullName FROM Employees
ORDER BY LastName, FirstName;

Other properties of the combo box would be:

BoundColumn    1
ColumnCount     2
ColumnWidths    0cm;8cm (or rough equivalent in inches but the first
dimension must be zero to hide the first, EmployeeID, column, so only the
name shows.

Ken Sheridan
Stafford, England