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