G'day
My mother-in-law had the same issue last year with her old Swiss notes. You will have to visit a branch of the Swiss National Bank to exchange them. No charges and you will get the full value in new bank notes. The closest branch is in Zurich town. The address is Börsenstrasse 15, 8022 Zürich. Open Monday to Friday 8 am to 3.30 pm.
The following link will inform you in more detail.
https://www.snb.ch/en/iabout/cash/id...instr_overview