Go to the S_ConsumableDetails and add the Use Starting Use Amount and set its type to Boolean. Then add Starting Use Amount and set it to Integer like the image below.
Now play in editor, it may take a while to load as it recompiles blueprints, once the player character loads you can exit play in editor.
Add the highlighted nodes shown in the image below, location at the top of the image and compile the blueprint.
Now click save all in the content browser.
You can now set items starting Use Amount in the Item List in their Consumable Details by ticking on Use Starting Use Amount and setting the Starting Use Amount value.