In this article we have learned that there is a powerful tool installed on ArchMerge i.e. downgrade. With this application you can downgrade an application in an easy way. You can see the picture at the bottom page how to downgrade firefox.
BUT when you do a clean install and you want to downgrade a package from AUR you will NOT have a cache file on your system and downgrade cannot provide support for AUR.
Then here is another solution for you to solve this issue. Normally I would explain to build the package but in this instance (pamac-aur) that will not work. I will explain an even easier solution.
Download the package from our github repo.
Go and look for the version you need i.e. pamac-aur-6.2.2-1-x86_64.pkg.tar.xz
or a later version if you need it.
and install it afterwards with
sudo pacman -U pamac-aur-6.2.2-1-x86_64.pkg.tar.xz
We need to edit following file and the following line
IgnorePkg = pamac-aur