Profile Workers can be added to a tenant in SAP Fieldglass by appropriate Buyer users or Supplier users.

When a user from the buyer side, who has the appropriate Profile Worker permissions enabled, wants to add a Profile Worker to their tenant, the first value they must choose is the Supplier name.
When a Supplier user, whose account has been configured to support Profile Worker functionality, wants to add a Profile Worker to their tenant, the first value they must choose is which Buyer to associate them to.