Sometimes Installer shows this error executing grub install dummy failed while installing grub and then you have to skip this most important step. The above commands are mandatory if grub was not installed during the kali installation.
However if grub is present in EFI system partition but entry of kali is missing from boot menu options then you don't have to do those efforts. Just select
Boot from EFI just below the Windows Boot Manager.
Click on the interface drive>EFI>kali>grubx64.efi
Once kali boots open terminal and enter these commands
sudo update-grub
sudo grub-install /dev/sda
For DELL users, there is no Boot from EFI option in your boot menu options but if you go to your BIOS settings you can add entry of bootloader in the table.