The app is called ATT presumably for attenuator but bizarrely they're also using the AT&T "death star" logo. They include a JPG of the logo including the AT&T text as well.
Even if they didn't supply the app, you could make a replacement very easily. It appears as a serial port and they describe the protocol on the auction page. It is very simple with only two commands where "r\n" returns the model number and "wvXXYY\n" sets the attenuator to XX.YYdB.