I embedded this to make other people's lives a little bit easier, the firmware you got my friend is the nothing but the normal bitmain firmware that can be found on their website here >
https://service.bitmain.com/support/download?product=Antminer%20S9the two versions that have this overclock/underclock functions built-in are
Antminer-S9-xilinx-201907311618-autofreq-user-Update2UBI-NF-sig.tar.gz
and
Antminer-S9-xilinx-201907302037-autofreq-user-Update2UBI-NF-sig.tar.gz
mind you that these two firmware versions have SSH access disabled by default, and you can't change the firmware once installed, unless you go through a recovery process using an SDcard.
if you don't care about SSH and don't plan on using any other firmware, those firmware are the best Bitmain ever made for S9 based on my personal experienced and opinion of course.