Who can use Randio
On a Shopify App Store install
Shopify decides who can open Randio. A staff member reaches the app only because you granted them app access in your Shopify admin, and that grant is the whole access decision: everyone who can open Randio has full access to it. There is no separate Randio login, no invitation, and no per-person role to set.
To stop someone using Randio, remove their access to the app in Shopify admin → Settings → Users.
Team users with roles
Randio also has its own user model: invitations, roles, per-feature permissions, two-factor authentication, and ownership transfer, managed on randio.app. It is used by custom plans with negotiated terms, where Randio administers the accounts. On those plans Settings has a Users & Permissions tab.
The pages that follow describe that model: Permission categories and Sensitive data access. If your store installed Randio from the App Store, they do not apply to you.
Related: Your plan.