If the member was added while Is Email Required? was No, the account was created with an internal placeholder address (not a real email), so it has no way to receive a login link and the member cannot sign in — the manager is expected to handle everything for them. To give the member their own login, an admin can open the member under Customers, enter a real Email and set a new Password directly on the profile, then save. Members added with a real email receive the New Created User email containing their login details when the account is created; check spam if it did not arrive, and confirm that email template is enabled under your email settings.