What's the procedure to uninstall Kanbo from Office 365 Trial account?

Please follow these steps:

1. Navigate to Site content in your site where you have added KanBo app and remove it.

2. Navigate to App Catalog in SharePoint admin center and remove app from Apps for SharePoint.

3. Navigate to App Permissions in SharePoint Admin center and remove KanBo app permission.

See more here: https://community.kanboapp.com/knowledge-bases/2/articles/806-uninstall-kanbo-from-office-365

Now you have removed al KanBo references from your Office 365. Azure part will be deleted automatically after 30 day.