How do i execute a change team script?

-How do i change the team of everyone in my game server from blue to red -How do i make it so that when the player dies then he changes back to blue team

You are going to have to set the AutoAssignable for blue to false.

function MoveToBlue()
    for _,Player in pairs(Game.Players:GetPlayers()) do
    --Looping through all players
        Player.TeamColor = BrickColor.new("Bright blue")
            --Change Team color
        Player.CharacterAdded:wait() --Make sure they are alive first
        Player.Character.Humanoid.Died:connect(function()
            --When they die
            Player.TeamColor = BrickColor.new("Bright red")
                    --Change back to red
        end)
    end
end

MoveToBlue()