PostFinance uses Swissquote as their broker. You can call PostFinance on 0848-888-710 (max. CHF 0.08/min in Switzerland) or from abroad you can call +41 58 667 99 85 (charged at telecom provider's international rate). From there you can follow the Swissquote guide located here.
Direct Register Shares from PostFinance
Updated: Jul 18, 2022