Questions for the Sixt representatives...

I'm looking at a car rental for a few days on an upcoming trip to Slovenia (picking up the car in downtown Ljubljana, dropping off a few days later in Portoroz downtown).

I see this offer on Sixt's website:

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Sixt - Partner with United.

Milage Plus
500 Mileage Plus miles per rental with Sixt rent a car worldwide

Special discounts for Mileage Plus members
Up to 10% discount on all rentals with Sixt rent a car and Sixt rent a truck** for Mileage Plus members

** On all offline and internet private customer rates of Sixt rent a car and Sixt rent a truck valid at time and place of rental. The discount depends on local availabilities and cannot be combined with specials.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Here are my questions:

1. I generally book through a local agent that I've used before. If I have my agent make this booking for me, can I still take advantage of this offer?

2. If yes, what specifically does my agent need to do to be sure I get the United Airlines miles and the 10% discount?

Thank you!