how to add interest to an overdue invoice in Quickbooks desktop and can it be automatically updated.

Hey there, @Dawn07. 

It's great to see you back in the Community! 

Creating a service item will allow you to add interest on the invoice in QBDT. Then add it to the second line when creating or editing the invoice. 

Here's how to create a service item for the overdue invoices: 

1. Go to the Lists and then Item List. 
2. Press CTRL + N and pick Service in the Type drop-down. 
3. Enter an Item Name and complete the Rate, Tax code, and Account. 
4. Hit OK when done. 

Review this guide for additional details: Add, edit, and delete items. 

Once done, add the service item you created in the second line in the invoice from. See the sample screenshot below for more reference: 

Feel free to come back if you need an extra hand managing your invoices. I'll be more than happy to assist you. Have a great day!