for a complete unisntall you should just be able to run sudo pacman -Rns <package_name> or yay -Rns <package_name> depending on how it is installed.
since you're doing a complete unsinstall and reinstall, you should be able to just run sudo pacman -Syu <package_name> or yay -Syu <package_name> and it will completely reinstall. If you are worried you have a corrupted download of the file, clear your package cache completely and run those commands, it should download a clean program install file and reinstall.
I'm not familiar with Mangohud and Goverlay, so unfortunately can not help our further, but maybe one of our other community members can.