video reference :

Even following the official tutorial from Odoo ( selecting all products ) is only helpful if maybe you have less than 100 products. I have over 1,000 products and definitely it'll get super-tedious to enter initial quantity one by one ... 

I'll try the "hack" solution as described above and as mentioned in several other threads

There is no "bulk/mass" editing available yet for Odoo huh ?

Hello Sergio,

You can use that tuto :

https://www.odoo.com/documentation/user/9.0/inventory/management/adjustment/initial_inventory.html

or that one:

http://odooservice.com/importing-product-quantity-update-inventory-in-odoo/

You have to import your stock from Inventory>Inventory Control>Inventory Adjustments.
To understand what you have to import, check on tutorials, or try to create an inventory with all products, and export it.

Regards,

FTK