There may be instances where a user must change their Zorin OS install from EFI to MBR (legacy) or MBR to EFI.
Often, this may be in order to ensure a consistent booting experience if more than one OS is installed. You want all installed OS's to preferably use the same Boot format.
To convert from MBR to EFI (Replace sdX with your actual drive I.D. like sda or nvme0n1...):
sudo grub-install --boot-directory=/boot --bootloader-id=ubuntu --target=x86_64-efi --efi-directory=/boot/efi /dev/sdX
To convert from EFI to MBR (Replace sdX with your actual drive I.D. like sda or nvme0n1...):
sudo grub-install --boot-directory=/boot --bootloader-id=ubuntu /dev/sdX
After running the command, be sure to run
sudo update-grub