Just download the PKGBUILD-<your-platform> (no need to download the whole repository), go to directory where you downloaded and type:

mv ./PKGBUILD-<your-platform> ./PKGBUILD
# use the below line if you need a DEBUG build
# sed -i 's/RelWithDebInfo/Debug/g' ./PKGBUILD
cd ..
makepkg -si

This will copy the PKGBUILD for your platform (where you type your platform name instead of <your-platform>), build it and install the PKGBUILD on 64-bit Archlinux ARM.

In the future, I might try to do an unified PKGBUILD for all platforms that will recognize your platform automatically.

All specified in COMPILE.md except for LARCH64, PPC64LE and SW64.

This might give you some advantages like:

• automatic updates (with some AUR frontends like pamac-aur or yay);
• easily uninstall with pacman -R when no needed (no need other scripts nor Makefile to do this);
• your box64 installation is recognized as a package (where it wasn't when installing with make install).