One of the methods of creating boxes in your FBA shipment is by using the "Box All with Case Qty" option
This can be very useful when your items have a default case qty. With this option you can set it up once, and then you can box up a shipment of numerous items with a single click of a button.
To be able to use this feature, you need to add the case qty for your SKU. You have the options to do it in bulk or individually.
Individually - In Shipping > Replenish Look for the "case qty" column and add the qty per below:
In bulk - go to Shipping > Replenish > Select Action > Update Bulk > Download the template and Fill out Columns A (SKU) and D (Case Qty), then re-upload the file.
Once your data is saved, reenter your shipment and press "Box All with Case Qty"