The procedure below outlines how to group the same products ordered on the eshop checkout page.

Procedure

1. Log in to the back office and go to Admin->Global Entity settings -> Eshop. 
2. Toggle Combine same products in EShop on and save the settings.
3. Clean up the back office cache to get the settings updated:  Go to Admin → Admin Catalog → Cleanup cache
4. Refresh the eshop page.
5. To disable this setting, just uncheck the option and continue with the rest of the steps.

This is available for CR version above 2.28.52 and eshop version 2.26.18

References