I’m not sure I fully understand what you’re trying to do, but I’ll give it my best.
The easiest method that I’m aware of is to right click, then select the “Show Text Editor” option. This will open up a new window section which contains an overview of all your diagram elements. The first tab displays all lifelines (actors and lifelines) and any extra information about them. The second tab shows all the messages in your diagram.
However, this section is merely an extra interface to edit parts of your sequence diagram.
If you want a full overview then I suggest you use the Glossary diagram. This will allow you to collect a series of names (basically model elements) and add them to an overview diagram (the glossary). Not only will this come much closer to what you want (or so I think), it also makes it easier to export this information in a more useful way to Excel (if you still need that).
Here is an example of what I mean:
Making this is really easy: double click on an element (in your sequence diagram) as if you were going to edit its name. When it is selected right click and then select “Add ‘name’ to Glossary” from the popup menu, where ‘name’ is of course your model element name. Do this for all the elements you need in the overview (I assume all the lifelines?).
Then go to your project browser (control-shift-b or click the icon on the right side of the screen (on the breadcrumb bar)). The Glossary will be shown in your Diagrams overview, and also in the Model Structure section (look for the ‘Glossary’ model):
This should make it really easy to keep an overview of all your model elements but in a grid-like fashion. If you want to export this to Excel then I suggest you use the ‘Raw’ export style. This will basically recreate the grid in Excel, which will make it much more accessible.
Hope this helped!