TurboTax is meant for use by individual taxpayers, not tax preparers, so there is no option to use Auto-Fill with the "Represent a client" option. You would need to use the taxpayer’s “My Account” login information to get information through Auto-Fill, or manually enter their information.

Please see this TurboTax FAQ for more details on how to use Auto-Fill in TurboTax Online: In online editions of TurboTax, how do I use CRA’s Auto-fill My Return service?

Thank you for choosing TurboTax.