I agree with David's response.
Thank you David.
Freddie, are you a PPM SaaS customer by chance? We do have a csv import utility for SaaS but it is for resource (user account) updates. You cannot create CA PPM resources (users) that you expect to also be able to log in through the CA On Demand portal. You would create new users who can log into CA PPM SaaS through the portal manually using ODUM, or the WSDL to update the portal. When you assign the user to one of your development, test, or production SaaS systems, the user is automatically created in CA PPM SaaS. You can use the CA PPM SaaS integration adaptor to update resource (user) information that cannot be brought in through the portal. See Add-in: Integration Adaptor (CA PPM SaaS Only) - CA PPM SaaS - 15.3 - CA Technologies Documentation
If not, you could use the REST API (unsupported) or the XOG (supported) or have CA Services setup or migrate user accounts for you. On-prem admins can manage user accounts directly in the application. See https://docops.ca.com/x/sZ-4G.
Let us know what you decided or if you had any further challenges. We hope you agree, the CA PPM Community is a great resource for sharing ideas and finding answers.