You can use a built in function of the menu editor for this. Go to your Custom Post Type in the Menu editor, click the “view all” tab and the first item you see is a link to the CPT archive page.
In case your CPT does not appear in the Menu editor please check whether your CPT has archives enabled ('has_archive' => true in the register_post_type-arguments).
When you are sure that archives are enabled and your CPT is still not visible you can reveal it through the Screen Options menu at the top of the screen (thanks, Nathan Hornby).
