New Record With Retaining Information

How to code this button so it creates a new record while retaining information such as a serial number. So if you pull up the item check out its past service. then you want to click a "new entry" button but you want the serial number to remain in the field.

What I got so far is:

Private Sub BtnAdd_Click()
On Error GoTo Err_BtnAdd_Click
DoCmd.GoToRecord , , acNewRec
Exit_BtnAdd_Click:
Exit Sub

Err_BtnAdd_Click:
MsgBox Err.Description
Resume Exit_BtnAdd_Click
End Sub

But obviously it erases the serial number.

The field is txtSerialNumber and the control source is SerialNumber.