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If your existing Schengen visa is expired, you must apply for a new one.
Because Switzerland is your "main destination", you must apply to the Swiss authorities.
Quoting the French embassy on the matter:
Previous grants of visas do no automatically qualify you for a renewal of the same or longer visa. A visa is never renewed or extended, each application is a new application. Your personal situation will be studied by the immigration officer each time you apply and the consular administration will determine if you qualify for a visa.