The authorities in Switzerland have asked you to provide a certificate of capacity in order for you to be able to exercise your civil rights, also known as a certificate of civil rights capacity. In Switzerland this is generally provided by the local authority in the place of domicile.
For legal reasons Swiss representations abroad are not entitled to provide a certificate of civil rights capacity to the Swiss Abroad.
You should therefore address your request to the authorities in your foreign domicile in order to receive this or an equivalent document.