How to customise WooCommerce Plugin jQuery Datepicker?

I have a wordpress website with WooCommerce installed and a plugin that provides custom fields on a product page. One of the options is a date picker. Although, the product sold is only available on specific days of the week (e.g. Monday and Wednesday). I understand how to get this effect, and an extensive google search gave me heaps of options. But I really don't understand where to put it, and how to override the plugin files. So, how do I edit the plugin's jQuery files to have specific days selectable in the date picker and where would I find the file to achieve this effect? I have been searching forever and decided to ask the community, and help is appreciated, thank you.