To mark all inventory items as drop ship items,
1.First create a saved search of the list of inventory items which are not marked drop shipped but have a preferred vendor and purchase price.
Criteria – type – inventory
drop ship item – no
preferred vendor – yes
purchase price – not empty
2.Export the list with the internal id of the items.
3. Extract the internal id of the items from the downloaded file and create an excel sheet
4. Add a new column – Drop ship item and enter ‘yes’ for all items and save the file as CSV
CSV IMPORT OF ITEMS
Import type – item and record type – inventory.
import option -data handling – update
In the field mapping mark the default value for drop ship item as yes

Now all the inventory items with a preferred vendor and purchase price will be marked drop ship item.