You need to purchase e-signatures first - I believe they are approximately $3 each.  After that you should be able to utilize the feature.  Simply highlight the client you wish to use and then attach the e-file authorization form first as the signature document and the return as the reference document (you can add additional items for signature as well but just hitting the basics here).  You add the signature and date blocks appropriately to the efile authorization form and then the program asks you to name the individual that is signing and the email address.  That is particularly important because only knowledge based authorization is cleared by the IRS for having this form e-signed.