Preliminaries

I am using Ubuntu 16.04. And now I want to change to other distro. However, after trying to boot from USB (with Arch iso) I had the error

Image failed to verify with *ACCESS DENIED*

The important thing is that I have no access to BIOS because I don't remember the password. So I cannot enable the Legacy mode. (I disabled Secure Mode with MOK utils but no success).

Problem

After numerous tries to boot from USB I (desparately) ran the command

apt install grub-efi-amd64

After that the above error occurs not only when I try to boot from USB, but also when I try to boot from my SSD. Now I cannot boot at all.

How to deal with that situation? I am not even interested in saving the data on the SSD. The main goal is to be able to boot my machine.

Thanks in advance.

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