For claiming process you can create simple contact form, for example: https://listeo.pro/claim-listing/
If necessary you can change listing ownership (assign listing to another user) with using “Quick Edit”:
Claim Listing Button
You can display in sidebar of each listing page a button that will redirects to claim listing form. To enable it go to Listeo Core → Single Listing and tick “Show “Claim it now” button on listing” option (you will have to configure also page to which button will be linked in Listeo Core → Pages).