You will need WP Directory Kit and WDK Membership plugin installed:

https://wpdirectorykit.com/plugin/wpdirectorykit/

https://wpdirectorykit.com/plugin/wp-directory-membership/

Login with administrator account

Enable WhatsApp in WDK Membership Settings:

Open listing preview page and click Edit in Elementor

Add WhatsApp on WDK Listing Agent element in Elementor

When you edit user account, you can enter WhatsApp number: