Hi there. 

I can’t imagine the hurdle you’ve been through concerning changing your employee's email when inviting in Workforce. 

Since you mentioned that the email address belongs to another employee that is already signed up for the workforce. Reaching out to our workforce chat support would be the best way to resolve this issue doing this can help them check your employee's email in the system to get this working. Just provide this link to them to communicate with our live chat support: QuickBooks Workforce.

For additional information about the process of updating your employee's information, feel free to visit this article: Update or delete employee info.

In QBDT, viewing your employee data and monitoring your business finances is easy. You can open any payroll reports that suit your needs. To give you a list of those reports and an overview of what data they show, please head to the Excel-based payroll reports page. 

If you need additional assistance updating your employee's email address, don't hesitate to post a reply below. I got your back. Have a good one.