Where do I find the PRO/Pack Upgrade button in Nebula CC?

Zyxel_JonasTan

Navigate to Organization-wide > License & Inventory.
In the "Overview" tab, you'll find the "Upgrade Now" button. Click it to upgrade to the PRO/Plus pack.

You may also refer to this link for detail information on how to upgrade your organization type from based to PRO/Plus pack.

If you encounter any other issues, please create a post here and tag @Zyxel_CSO, or simply create a ticket directly.