Found it:

Private Sub CommandSearch_Click()
    
    'use DAO when working with Access, use ADO in other cases
    Dim db As DAO.Database
    Dim rs As DAO.Recordset
    Dim sql As String
        
    'eerst een check of het zoekveld niet leeg is
    If Nz(Me.txtSearch.Value, "") = "" Then
        MsgBox "Geef een bestelbon in !!", vbExclamation
        Debug.Print "Geef een bestelbon in !!"
        Exit Sub
    Else


    ' Define your SQL query
    sql = "SELECT [Transporteur], [Productnaam], [Tank] FROM [Planning] WHERE [Bestelbon] = " & Me.txtSearch & ""

    ' Set database and recordset
    Set db = CurrentDb
    Set rs = db.OpenRecordset(sql)

    Me.txtResult.Value = rs!Transporteur
    Me.txtProduct.Value = rs!Productnaam
    Me.txtTank.Value = rs!Tank
    
    ' Clean up
    rs.Close
    
    End If
    
    Set rs = Nothing
    Set db = Nothing
    
End Sub