Private Sub CmbCourse_Click()
    strCrs = "(course=" & Str(CmbCourse.ListIndex +  1 ) & ")"
    useFilter
End Sub
Private Sub CmbGroup_Click(Area As Integer)

    If Not (CmbGroup.SelectedItem) Then
        strGrp = "(group=" & Str(CmbGroup.SelectedItem) & ")"
        useFilter
   End If

End Sub
Sub useFilter()
    Dim StrS As String
    If Trim(strCrs) <> "" Then
        If Trim(strGrp) <> "" Then
            StrS = strGrp & " and " & strCrs
        Else
            StrS = strCrs
        End If

    Else
        StrS = strGrp
    End If

    adoRs.Filter = StrS
 
    Set cmbUser.DataSource = adoRs
    Set cmbUser.RowSource = adoRs
    cmbUser.BoundColumn = "id"
    cmbUser.ListField = "FIO"
            
    cmbUser.ReFill
    cmbUser.Refresh
End Sub 

The Filter property of the original Recordset, if any, will not be applied to the clone. Set the Filter property of the new Recordset in order to filter the results. The simplest way to copy any existing Filter value is to assign it directly, like this: rsNew.Filter = rsOriginal.Filter