spreadr-hidden tag can be added via 2 methods:
1. Via Spreadr Dashboard
a. Login to Spreadr Dashboard
b. Goto 'Settings' page
c. Click 'Default Values'
d. Add spreadr-hidden tag in the Tags field
All products which you now import from Amazon will have spreadr-hidden tag added to them.
2. Via Shopify Dashboard (for products already imported via Spreadr)
a. In Shopify dashboard goto the product page where you want to apply spreadr-hidden tag
b. Look for Tags input section
c. Add spreadr-hidden tag
Repeat for all products for which you do not want 'View on Amazon' button.