That is problem with product and service cost not be update win insert new bill make me not know exact cost .

Welcome to the Community, @computerstar2020.

You can easily track your product and services cost once you've entered the necessary information manually in QuickBooks. 

Here's how:

1. Go to the Gear Icon and select Products and Services under Lists.
2. Update your items by clicking the Edit option.
3. Be sure to enter the amount on the Cost field.
4. Click Save and close when done.

This will only update the newly created bills, the tracking won't be applied to your previous transactions. You can also check this helpful article to help you manage your inventory in QuickBooks: Set up Products and Services.

If this isn't what you're referring to, please let me know. Any additional details would be greatly appreciated so I can provide you with the right information.

As always, I'm here to help if you have other questions. I hope you have a good weekend.