From pacman (root only)

pacman -U file:///var/cache/pacman/pkg/package-old_version.pkg.tar.zst

From AUR

git clone https://aur.archlinux.org/package.git
cd package
git log -m -p

• Récupérer la version et le checksum de ce qui vous intéresse.
• Corrigez le PKGBUIILD

Puis enfin :

makepkg -sri

• -s − Install missing dependencies using pacman. When build-time or run-time dependencies are not found, pacman will try to resolve them. If successful, the missing packages will be downloaded and installed.
• -r − Upon successful build, remove any dependencies installed by makepkg during dependency auto-resolution and installation when using -s.
• -i − Install or upgrade the package after a successful build using pacman.