The FAQ you linked to is specifically for deleting all of the data for a specific website. These steps are usually only performed if you want to delete the data without deleting the entire site.
For deleting an individual site you can follow the steps in our FAQ here: https://matomo.org/faq/how-to/create-and-manage-websites/#update-and-delete-websites
If you want to delete just the data for a site as mentioned in the FAQ you linked to, then you would need to reach out to our Cloud support mailbox at support(at)matomo.cloud
You can also alternatively delete some or all data for a site using the GDPR Privacy tools: https://matomo.org/faq/how-to/how-do-i-delete-rows-of-a-report-and-specific-visits-to-clean-up-some-of-the-reporting-data/
I trust this information will be useful to you.