The plugin includes a shortcode to show the one-click button, so you can display it wherever you want. The shortcode is:
[yith_wocc_button]
And following you find the attributes:
product-Set the product ID that has to be purchased. If no ID is set, it will automatically load the global product, if any.label-Set the button text. If no label is set, the plugin will automatically load the default label text that has been set in the General options as explained here.