You can use the Symbols panel (Window > Symbols) or the Control panel to manage the symbols for a document. The Symbols panel contains a variety of preset symbols. You can add symbols from symbol libraries or libraries that you create.
Duplicating or copying a symbol in the Symbols panel is an easy way to create a new symbol based on an existing symbol.
Select a symbol in the Symbols panel and choose Duplicate Symbol from the panel menu, or drag the symbol onto the New Symbol button.
Select a symbol instance and click Duplicate in the Control panel.