No apologies necessary. In fact, when it comes to adding custom buttons to product pages, I may be even more ignorant than you! I’ve no idea what you did to add them, so cannot advise on how to alter class attributes. It might be easier said than done.
What is maybe feasible if altering the class is difficult is to add all the necessary CSS overrides that will style the link as desired. The risk in doing so is if it’s not done thoughtfully, this could also inadvertently affect other links we don’t want to alter. In any case, it’s preferable to have the correct HTML to start with instead of patching it up with CSS.
The easiest way to add HTML to product pages is to include it in one of the description fields, but then you’re limited to where the HTML will occur. WooCommerce does offer a lot of action hooks we can use. Using them does require some custom coding though. It’s not all that complicated of code, some people have managed to do it with little experience. They copy/paste examples they’ve found and do some minor editing.
Another way is with template overrides, but this approach is less than desirable. Best left for when the hook method will not accommodate a need. There may be other ways through helper plugins that I’m unaware of.
I can only speak in generalities, I don’t have a lot of WooCommerce experience. If you need more specific advice, I think their dedicated support forum is the best place to seek guidance. I cannot advise on what you should do from here, but those are your basic options AFAIK.