How do you use the left side of the mouse to move the camera?

Does anyone know how to rotate the camera with left click? Here's the script's i'm trying to edit.

local function OnMouse2Down(input, processed)
		if processed then return end

		isRightMouseDown = true
		OnMousePanButtonPressed(input, processed)
	end

	local function OnMouse2Up(input, processed)
		isRightMouseDown = false
		OnMousePanButtonReleased(input, processed)
	end

	local function Button1Down(input, processed)
		if processed then return end

		isMiddleMouseDown = true
		OnMousePanButtonPressed(input, processed)
	end

	local function OnMouse3Up(input, processed)
		isMiddleMouseDown = false
		OnMousePanButtonReleased(input, processed)
	end