In this howto there are the steps to follow when a Windows 10 OS is not bootable anymore and you haven’t a recovery disk. This is a typical case after a new OS will be installed on Dual boot or boot partition was altered.

1. 1. Download Windows 10 iso:
      1. Download the official Windows 10 image
   2. Prepare USB to be bootable:
      1. Open GParted with

         gparted /dev/DEVICE-TO-ERASE
         

      2. Select the USB drive
      3. Device > New partition table
      4. Select GPT
      5. Apply: this will delete any data on the USB
      6. Create a new NTFS partition then Apply (do not use FAT32 since some files can be greater than 4GB)
      7. Close GParted
   3. Write files:
      1. Unplug and plug USB
      2. Copy all Windows files to the empty USB drive using 7zip with:

         7z x -y -o/media/user/path-to-USB/ Win10_1809Oct_Italian_x64.iso

      3. If something goes wrong during copy, you can mount the ISO image then rsync the source with the USB drive (the trailing slash is important):

         cd path/to/usb/drive
         rsync -avzp /media/myuser/CCCOMA_X64FRE_IT-IT_DV91/ .
         

      4. umount
   4. Add boot flag
      1. Open the
      2. Select the new partition then
      3. Select Partition > Manage flags
      4. Select boot flag (esp will be auto-selected)

1. Use windows tools
   1. Follow this howto by MS to recover MBR, restore BCD or similar actions

You can follow these steps to write on a USB a recovery ISO from windows the same way.