Change Stock Amount?

Hi
To do an individual product:
Go to ‘products’
Open the product. go to ‘Inventory’
Set the amount in stock.

To do a whole lot at once:
Select all the products with the tickbox at the top of the list, then click ‘bulk actions’ and ‘edit’. Now click ‘apply’.
You’ll get a form with lots of fields on it. RH side, 2/3 way down there’s one called Stock Qty. click it and set a new value. Hit ‘Update’ and you’re done.

If you want to only have one, is that because you actually don’t want to manage stock with WooCommerce? If that’s the case, in stead of adding a quantity, click the box ‘Manage Stock?’ and select no. this will remove all ‘out-of-stock’ warnings etc.

Hope that helps?