You messed this team rather than fixing it. Offensive Eternatus runs Life Orb / Power Herb, not Black Sludge as it needs power, not longevity. Even though there's Geomancy Xerneas, Dusk Mane Necro and Blissey are its best counters; as well as Eternatus doesn't let it set-up by OHKOing by Sludge Bomb before.
No one runs Tornadus/Thundurus in Ubers, and in case of Landorus-T even Zygarde just hard walls it. Magnet Rise is a perfectly fine choice, as it lets it set on Earthquake Dusk Mane, Groudon, etc. Fusion Bolt isn't better than Bolt Strike, as power is more important here than accuracy.
Did you even know what Utility Umbrella does before telling to change it? It makes it ignore Kyogre's rain based effects, which means Choice Specs Spout doesn't 2HKO. And, Blissey is better than Eviolite Chansey because it can hold a item; this case Utility Umbrella to not lose to Specs Kyogre. Please learn a bit more about Ubers before suggesting changes.