Expired client certificate

my NextCloud server requires a TLS client certificate to establish the connection. In the Desktop Client this was configured using the “Configure client-side TLS cert” option during first setup. The client certificate is now expired. The desktop client shows: “Error while reading: error:14094415:SSL routines:ssl3_read_bytes:sslv3 alert certificate expired”. How can I configure a new client certificate for the connection?

The only hint I could find is How to remove a certificate exception where deleting the cookies0.db is recommended. However, I don’t want to have to re-sync all files.

Many thanks for the help!