Hi there, @In2theBlueSky. I'll help you add these lists in just a few clicks.

First, we can export the customer, vendor, and items list. This way, you can import them back to your new company file.

Export the data from the existing file

1. Go to the File menu and select Utilities then Export.
2. Choose Export IIF Files.
3. From the Save in the drop-down, select the location you want to save the IIF. For example, your Windows desktop.
4. Enter a name in the File name field and select Save.
5. Tap OK.
    

Import data to the new company file

1. Go to the File menu and scroll-down to Utilities.
2. Hit Import and select IIF Files.
3. Tap Import IIF file.
4. Look for the file that you saved from the other company and click Open.
5. Follow the succeeding prompts to import the file.
    

Check out these articles for more details:

• Import Or Export MS Excel Files
• Import And Export Data In QuickBooks Desktop

We can also take a look at this article for more information: Create QuickBooks Desktop Company file: Overview.

Please post again in the Community if you have follow-up questions. I’ll be here to help. Take care and have a good one!