Auto adding waregouse to the new item

Hi experts.

I have an issue related to the auto adding of the whse to the new item, i havent selected this option in the general setting because of this the whse are not added to some 23000 items, this also stopped me loading the openings.

please suggest the best way to select whse in the item masters as it would take too much time to add whses one by one.

thanks & regards