Rattigan350:
You are doing something JWs commonly do, which is mix up two very old Christian doctrines, namely the Protoevangelium, and the other which is actually the Catholic and Greek Orthodox interpretation/devotion involving St. Michael the Archangel--which Watchtower leans on when trying to defend its "Jesus=Michael" doctrine.
The idea that Genesis 3:15 is some type of prediction of Jesus' coming is a teaching stretching back to the late Church Fathers called the Protoevangelium or the "First Gospel." The doctrine is that Mary is the "woman," Jesus is the "seed," and the Devil is the "serpent." It is not a Jewish teaching as there is no belief in Satan the Devil in Judaism.
Revelation 12:7 deals with an entirely different serpent, namely Leviathan, as Revelation is using Jewish tropes, not Christian ones. The Protoevangelium was first established in 180 CE, the late 2nd century, by Irenaeus, and Revelation was written around 95-96 CE, the late 1st century. So the "original serpent" could not have been the idea of Irenaeus' Protoevangelium as it had not yet been invented when Revelation was written. The author had to have something else in mind as this was a doctrine to come later after the book came about.
So before this Christian doctrine was created, the only other "original serpent" there could be (since the Jews did not believe that Genesis chapter 3 was Satan the Devil") was "leviathan" of Isaiah 27:1. Of this scholars are in agreement. Just do an Internet search and you will see that academics agree that this is the actual connection:
We know that Revelation is not recalling the snake in Eden because the source of John’s language isn’t Genesis, it’s Isaiah. Along with calling the devil a “serpent” (ophis; ὄφις), Revelation 12:9 describes Satan as a “dragon” (drakon; δράκων) three times. The only other verse in all of Scripture that describes a creature as both a “dragon” and a “serpent” in this way is Isaiah 27:1, and the creature is the primordial sea-monster known as Leviathan. The Isaiah verse appears in the context of God's eschatological battle against evil, which is the very same context that readers encounter in Revelation when Michael and his angels confront Satan (see Rev 12:7-9). According to the Greek translation of the Hebrew Bible, Isaiah 27:1 states, “In that day God shall bring a holy and great and strong sword against the dragon (drakon; δράκων), the serpent (ophis; ὄφις) that flees, upon the dragon (drakon; δράκων), the twisting serpent (ophis; ὄφις): [God] shall destroy the dragon (drakon; δράκων).” Revelation 12:9 contains the same threefold repetition of "dragon" that appears in Isaiah 27:1, and both verses repeat the word alongside "serpent" in the context of divine battle. Therefore, we can be confident that Isaiah 27:1 is the verse to which Revelation refers in its description of heavenly war against Satan.--Which "Serpent" Is Satan? Israel Bible Center.
Watchtower leans upon Catholic views of Michael as a warrior against the Devil, usually with a sword and the main leader of God's forces against Satan popular in the main public's view, to play on the religiously uneducated to suggest that only Jesus Christ could play this part in God's plan.
The famous prayer to St. Michael the Archangel is quite unknown to Jehovah's Witnesses, but it sounds like actions that only Jesus Christ would play as one conquering the Devil:
St. Michael the Archangel, defend us in battle, be our protection against the wickedness and snares of the devil. May God rebuke him we humbly pray; and do thou, O Prince of the Heavenly host, by the power of God, cast into hell Satan and all the evil spirits who prowl about the world seeking the ruin of souls. Amen.
Watchtower doctrine is "mushed-up" beliefs of Christology, mistaken identities, and uneducated Bible look-ups with a little popular mythology added in since no one seems to know any better.
(IMHO, JWs are often too afraid to purchase or read one of Christendom's or Judaism's Bibles for fear "evil" or academia might "rub off" on them--but they would just learn the above if they did. This isn't something you would learn in a college course, just from a sidebar or a footnote in your average Bible.)