See how you can edit a symbol from the main Timeline by double clicking the INSTANCE of the Library symbol on the Stage.

It is important to know how to get IN the symbol to edit it, but also how to come back to the timeline (upper right arrow)
If you are a clumpsy clicker, you might find yourself more than once inside a symbol and quite confused.

You can also edit a Symbol by double-clicking the symbol on the Library window (double click the little graphic-icon or the Preview on the Library)

If you edit the symbol this way, you will not see the relative position of the element on the Stage: you will only see the symbol content.