Minecraft.net site, in your Minecraft launcher, or inside a special “carnival-themed” map in Minecraft Bedrock edition.
To vote inside your game launcher, look for the left sidebar tab called “Minecraft Live” next to all your owned Mojang games. You'll be able to make your choice right there on that launcher tab.
To vote in-game, open Minecraft for Windows from your launcher and look for the “Mob Vote” button on the left side of your main menu to join the world where you can check out all three mobs and vote for your favorite.
There is no voting on Twitter this year, which means you can change your mind about your vote right up until the deadline and also that the results will be a secret until revealed, unlike public polls on Twitter.
What mobs are in the mob vote?
Like past years, there are three potential new mobs to vote for this year: the Rascal, Tuff Golem, and Sniffer. Mojang has given some details about each to help make up your mind.