Installation video available on the support site for your Electric Longtail Cargo Bike R500E:
https://support.decathlon.fr/velocargo-r500-e-notice-reparation-couleurs-vert-beige-et-rouge
Direct link to the DIY video:
https://players.brightcove.net/3415345270001/mBbJuV35H_default/index.html?videoId=ref:p2539304_1