I want to associate my new vehicle with Communauto?

There is no automatic support transfer procedure for the Communauto service. The access medium used is the one registered when I registered with Communauto.

To modify my access medium or obtain information on compatible media, I can contact Communauto Paris directly:
Phone : 01 72 09 07 75
Website: https://paris.communauto.com/contact 

To date, the Navigo pass on smartphones is not compatible with the Communauto service.

I can also consult the Communauto FAQ published by Île-de-France Mobilités:
https://www.iledefrance-mobilites.fr/aide-et-contacts/autopartage/utiliser-service-autopartage-communauto-dans-application-ile-de-france-mobilites