Nowtry booting from the USB, and see if you get the altered menu item,and that it works. When the USB boot is working, you may simply goto /boot/efi/EFI/Boot, which should be the hard disk's EFI partition, andit should contain copies (possibly with different names) of the Ubuntuversions of the boot files, which should also be in /boot/efi/EFI/ubuntu.
Use md5sum to confirm that you have copies of all files which are in /boot/efi/EFI/Boot, because you are going to delete them! Copy andrename the file /boot/efi/EFI/Microsoft/bootxmgfw.efi to /boot/efi/EFI/Boot/bootx64.efiand you should be able to boot windows from the hard disk again -- removethe stick and try the Windows boot.