Comment 580 for bug 1734147

#579

As I have way less experience with EFI than legacy BIOS, I hesitated to add my comment.
But there seems to be no answer to your question so far, I'll add my 2 cents.

If you can still boot from your Windows installation, there is a hope.
You should be able to proceed as in the legacy BIOS setting (see above postings) but use GRUB2 instead of EasyBCD.
The detail is explained at EasyBCD website:
https://neosmart.net/wiki/easybcd/uefi/
Option 3: Use GRUB2 EFI as your main boot manager

While I cannot guarantee the result, it is worth trying before resorting to the hardware solution (replacing or reflashing ROM chip).