just use CFrame.RightVector and multiply it by a negative number, since it'll be the opposite of RightVector, as theres no LeftVector. also why are use creating a variable thats defined as the player's UpperTorso, and not using it.
game.ReplicatedStorage.Roll.OnServerEvent:Connect(function(plr, char)
local uppertorso = char.UpperTorso
uppertorso.CFrame = uppertorso.CFrame + uppertorso.CFrame.RightVector * -10
end)
also you cant send instances through arguments in OnServerEvent, so just set the cframe on the client, because it would replicate. or if you wanted it to move to the left instead of teleporting use MoveTo().
character.Humanoid:MoveTo(character.HumanoidRootPart.CFrame.Position + character.HumanoidRootPart.CFrame.RightVector * -10)