First, you need a KOS Studio account. You can contact an administrator of the organization request an invite both to KOS Studio and to the specific organizations. Invites are limited to organization scope, and within organizations, admins can choose which projects are visible to you. Once you get an email with the invite just follow the steps in the email: create an account with the token, login, you will see all available organizations and projects.

You can learn more here: User Management