Select an instance of it and right-click, the context-menu item 'Save_As' then exports that component to a chosen location. A similar method is also available even if there are no instances - in the Component Browser hover over its icon in the Model pane and right-click again you have 'Save_As' again...
To use that component in another model use File > Import, or if it's in a folder in you Components' paths then pick it from there in the Component Browser.
Another way is to Edit > Copy an instance and then in the other model's window Edit > Paste [you choose the location] or Edit > Paste_in_Place to put it exactly where it was in the original model...
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