How to pass username for SAML login through servicenow?

Using okta with servicenow configured as per this document How-to-Configure-SAML-2.0-for-ServiceNow. When a user is redirected to okta login how can I auto populate their username?

Hi @sunfish! Please open a support ticket through an email to support@okta.com with this issue. One of our Support Engineers will be happy to assist you further.