How to install previous firmware

Hello .

I updated my pixhawk ardupilot (quad x) from 3.6.4 to 3.6.5 , but 3.6.5 makes big yaw drift, so I would like to rollback to 3.6.4 .
I tried to rollback to 3.6.4 with mission plannner, but “pick previous firmware” pull down list does not show 3.6.4 .
So I looked for firmware file distribution site, and I have two questions.

(1) What is suitable firmware name for Pixhawk 2.4.8 ? Firmware distribution page has many hardware names. For example, fmuv2, Pixhawk4, PX4 or and so on.
(2) What is certain build time for 3.6.4 ? Firmware distribution page has many build time stamps.

Thank you.

@otk1fd if you want NuttX version, its px4-v2 and fmuv2 for ChibiOS. And, for your second question it depends on the system. It takes about 4-5 minutes on my laptop.

Thank you your response!

I am using chibios, so I will choose fmuv2.

At second answer, I have no enough skill to build on my PC.
So I would like to install prebuilt binary.
According to GitHub commit history, 3.6.4 was build on 27 December 2018.
But firmware distribution page has four directories that is named to build time.
I cannot identify build time.

Thank you.

I found easy step by step guide page.
I will try it.

I build firmware but hash value of exported *.apj file does not match to prebuilt firmwares that is built on 2018/12/27.

@otk1fd once you clone the repo, you can do

git checkout Copter-3.6.4
git submodule update --recursive

then build it. The hash value should be 6c4da9e3