Try this code to pick a file from a SharePoint site:
Dim SummaryWB As Workbook
Dim vrtSelectedItem As Variant
With Application.FileDialog(msoFileDialogOpen)
.InitialFileName = "https://sharepoint.com/team/folder" & "\"
.AllowMultiSelect = False
.Show
For Each vrtSelectedItem In .SelectedItems
Set SummaryWB = Workbooks.Open(vrtSelectedItem)
Next
End With
If SummaryWB Is Nothing then Exit Sub
If I remember correctly, the Microsoft Scripting Runtime
reference must be enabled. Also, your site may use backslashes, mine uses forward slashes.