Removing 'Back to Store' link
If you create a Custom Page and use Link Sets you will not want the 'Back to Store' link to appear on the Product Details page
Back to Store link as it appears
Scroll down to Store > 'Show Back to Store Link' and disable
Add a Text Link to the Product Description
Go to each Product Description field
Manually add (copy and paste) a snippet of text like '< Back to Store' that can have a link added.
Tap 'Link' icon that appears when text to link is selected
Create a Link
Tap 'Choose a page' dropdown
Select the Page Title that you are using for your Store with Custom Pages and Link Sets.
View Live Product
How the '< Back to Store' link will appear on your live site.