- Open Notepad with Administrator priviledges,
- Navigate to C:\Program Files\Citrix\Web Studio\Site on Web Studio server,
- Edit the file named projects_mainapp_src_bootstrap_ts.[hash].js,
- Search for this.domain="", there are 2 matches,
- Add your required domain between quotes.
https://support.citrix.com/article/CTX571840/how-to-prepopulate-domain-name-in-citrix-web-studio-logon-page