Revelation 22:13 in the New World Translation reads:
"I am the Alʹpha and the O·meʹga, the first and the last, the beginning and the end."
So the "Alpha and the Omega" is calling Himself "the first and the last," and "the beginning and the end."
Revelation 1:8 in the New World Translation reads:
"I am the Alʹpha and the O·meʹga,' says Jehovah God, 'the One who is and who was and who is coming, the Almighty."
So "Alpha and the Omega" = "the first and the last" = "Jehovah God."
Revelation 1:17-18 in the New World Translation reads:
"When I saw him, I fell as dead at his feet. And he laid his right hand on me and said: 'Do not be afraid. I am the First and the Last, and the living one, and I became dead, but look! I am living forever and ever, and I have the keys of death and of the Grave."
So "the First and the Last," who is Jehovah God, said, "I became dead."
When did Jehovah God die? The answer is found by clicking on the superscript "n" or "+" just after the phrase "I became dead" in Revelation 1:18 and looking on the right side of this page to read:
"1 Peter 3:18 For Christ died once for all time for sins, a righteous person for unrighteous ones, in order to lead you to God. He was put to death in the flesh but made alive in the spirit."
Since Jehovah said "I became dead" to refer to the death of "Christ," "Jehovah" also refers to "Christ."