Grub Customizer is not available for Windows but there are some alternatives that runs on Windows with similar functionality. The best Windows alternative is EasyBCD. It's not free, so if you're looking for a free alternative, you could try EasyBCD or EasyUEFI. If that doesn't suit you, our users have ranked more than 10 alternatives to Grub Customizer and ten of them are available for Windows so hopefully you can find a suitable replacement. Other interesting Windows alternatives to Grub Customizer are Grub2Win, iReboot, GRUB4DOS and WINGRUB and BootIt Bare Metal.
It runs its own operating system directly from the boot partition where it is installed, therefore not needing either Windows or Linux to load before you can configure everything. It also means it can fix itself, without loading an OS, if anything goes wrong. And if the boot partition itself gets messed up, it can automatically fix itself from the original installation pendrive.