For using a JTAG programmer cable on the Xilinx Artix-7 FPGA found on the Sparkfun Alchitry Au(+) boards you will need access to its JTAG pins: TMS, TDI, TDO and TCK.
Fortunately these are accessible through the Bank D connector. For ease of use I have used the Alchitry Br breakout board and mounted a 6 pin Xilinx and Digilent compatible header on the patch aria.
Simply connect the Artix-7 JTAG pins, Vcc (3V3) and ground to the header completes the job

In the attached pdf file I will give you more details and I will show you how to use it in Vivado.