Hi,
I already told you in my first message here:
You could activate it with the "Display a contact button on the product page" setting of the HikaShop configuration and then use a translation override in order to change the text of the button:
www.hikashop.com/download/languages.html#modify
Were you not able to find that "Display a contact button on the product page" setting in the HikaShop configuration ?
And to change it, please read the explanations of the link I gave on how to create translation overrides.