I prefer doing it in VBA - you have more control over various things...
Here is a code that queries a "Training Dates" table, and returns records that match "TestDate" with the selection in a listbox, then it updates the field named "NewDate" to today's date.
I typed some of this freehand, so you might have to correct some things. It's also good to do some error handling, and checking to ensure their is a record (or if it returns multiple records...)
Code:
Dim db As DAO.Database
Dim rs1 As DAO.Recordset
Dim sql1 As String
sql1 = "select * from [Training Dates] Where [TestDate] = " & """" & me.listbox.value & """"
Set db = CurrentDb
Set rs1 = db.OpenRecordset(sql1)
rs1.MoveFirst
rs1.Edit
rs1![NewDate] = Now()
rs1.Update
rs1.Close
Set rs1 = Nothing
db.Close
Set db = Nothing