If your identity doesn't exist, there is nobody to die. It's one of those things that mostly makes sense if you've experienced it. For the record I wouldn't recommend it. Premature annihilation of ego can lead to shunyatta poisoning, or emptiness poisoning. The ego causes issues for sure, but if you kill it before you cultivate a deep understanding of compassion you can easily become a genuine villain.

I understood it.

"Ego death" is the removal of a sense of self as distinct entity.

Since the self no longer exists as a distinct entity, and since we regard death as the end of self, it becomes impossible to be afraid of death as death is no longer relevant.