If you are looking to mass delete check marks “Show in Webshop” on product card, then this is how you should processed. 

1.  PIM - Export products - Export your product catalog, the you have a list of all your products in excel and can see which products are visible in Webshop and which not (Show in Webshop column) 
2. In the excel replace the Show in Webshop column “yes” values with “no”. 
3. Leave only Product code or ID and Show in Webshop column in the file and save.
4. Now upload the file in the product Importer PIM - Import Products

Updating Process: 

• PIM - Import Products
• Update Products 
• Upload the file, either XLSX or CSV format
• File has headers
• Create

Configuration: 

• Match existing products by Product Code or ID or both
• Select Operation Update

Mapping: 

• Choose the column names 
• Apply and validate configuration
• Make sure the row is marked yellow and Update in the Action column
• Confirm and start import

After Import in finished open the product card and see that the “Show in Webshop” option is unmarked.