As a part of the insurance cover with Allianz, you will be asked to complete a form called a “Déclaration Relative Aux Bénéficiaires Effectifs”. It is basically a replication of your KBIS document with an additional signature.
Download an English translation here: https://francemotorhomesales.com/wp-content/uploads/2023/06/Allianz-SC-form-ENG.pdf
Fill out the original French PDF: download here
Simply copy over the main details of your societe civile for the top section, then write in the partners in the sections below then sign the second page.