You can continue using the email address you used from your previous employer to QuickBooks Workforce. May I know, do you still have access to that account? If so, please use your existing credentials when accepting the new invitation. Then, ensure you accept the most recent email.
For further details, you can refer to this article: Troubleshoot sign-in issues for QuickBooks Workforce.
Please also note that if you have already used this email for your QuickBooks Online account, you will need to provide a different email address for Workforce, as the two cannot share the same login.
Feel free to reply below if you have follow-up questions.
