Hi,
The text of the button on the product page is something that you added yourself to the HikaShop via a customization of one of the views of HikaShop.
So you should actually know better than us how to change it.
It has to be in one of the view files of the view "product", but I can't say exactly.
Rgearding the contact form page, that's the joomla contact form. You need to edit the joomla view file for that. You can't do it via HikaShop. You neeed to edit it via FTP. It should be one of the files in the folder components/com_contact/views/contact/tmpl