Please add your issue as a new post and not bumping a previous thread.
You can’t change the design of the read more text in the Wix Store Product Page as it is part of the Wix Stores setup, you can only edit all as shown here.
https://support.wix.com/en/article/customizing-your-wix-stores-product-page
You will have to add your own text box and button to add your own show more option as stated in the tutorial for it.