Whenver you establish a picker control you will inexorably connected it to a data source via a smartobject. Now when you do this there will be an option to select the identifier.

The identifier is the field that the SmartObject method you select will use to retrieve the desired outputs.  In this particular case I have chosen an AAD User SMO as the data source and the Get List method. Here are the identifiers I have to select from:

You will notice that 'Account' is highlighted. Be warned; this is not a valid identifier with the Get List method. That method does not use this field that identifier is a product of the 'Get Direct Reports' method. All possible identifiers of all the SmartObject's methods are surfaced in the identifier drop down so ensure you chose appropriatly.