Hi,

the responsivizer template has already a mobile 'hamburger' menu in various format so you don't need the one used for desktop template. Refer to the PDF docs at the paragraph 'Mobile menu positions and management'

If you think to have a mobile menu used on desktop that will work well even on mobile and it's a separate Joomla module, you can even try to use it on the responsivizer template. Just assign it to a responsivizer template position.

Obviously if you need different/more items for a mobile menu you have to create a new menu in Joomla.