Login as AI Risk and Compliance Admin and open Workspace Admin. 

Open the relevant assessment template(AI impact assessment in this case) and publish the template.

Log back in as AI Product Owner and check if you are able to start the assessment.

If you then observe the error "Incorrect setup. Contact your administrator", follow the steps mentioned in https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB3006366

Hope this helps