Hello,
Navigate to WooCommerce > Settings > Products and click on the Inventory link from the top. Enable the Manage stock checkbox and set basic stock management settings: https://ibb.co/LXnPPG0K
In addition to this, WooCommerce also lets you manage stock at the product variation level. To do this, navigate to the variable product’s edit page. Then click on the Variations tab under the Product data metabox.
From here, you can choose the variation you want to manage stock for and tick the Manage stock? checkbox to view the Stock quantity field. You can manage stock for each variation following this method: https://ibb.co/7TyTL2C
Best Regards,