Hello there, grace_yew,
You can directly go to the inventory item and edit the cost. Here's how:
- Click the Gear icon.
- Select Products and Services.
- Locate the item, then click Edit under the ACTION column.
- Scroll down to see the Cost box, enter the new amount.
- Click Save and close.
Here's an article on how to use reports to see your sales and inventory status: https://community.intuit.com/articles/1790411.
If you have other concerns related to inventory, don't hesitate to post a question.