You will receive the error: "Your account is managed by your employer. Please contact your IT department to change your role or password" if your organization has SSO enabled.
In order to change a users role with SSO enabled, you would need to have their roles updated via the IDP assertion which is detailed in step 1 of our Help Center documentation here: SAML SSO
When logging in via SSO, and not directly via the platform, a user's account and role is derived from the SSO and as such it is not possible to amend this directly from the platform itself. It needs to be edited in your IDP.