You can use the Verify and Rebuild tools in QuickBooks Desktop (QBDT) to fix the issue where your net 60 terms reverted to net 30, @Kate0925.
 
Before doing so, please update QuickBooks Desktop to the latest release. Keeping your software up to date allows you to access the newest features and enhancements. Once updated, use the Verify Data tool to identify any issues within your company file.
 
Here's how:
 
 - Select Utilities from the File section in your account.
- Choose Verify Data. If there's an error message, you can search it on the QuickBooks Desktop support site  for how to fix it.
 
If you see that your data has lost integrity, rebuild your company file to fix it. You can follow the detailed steps in the Rebuild your company file data section of the Verify and Rebuild Data in QuickBooks Desktop article.
 
After rebuilding, restart the software and attempt to create an invoice to verify if the terms default correctly to net 60 instead of net 30.
 
If you have any other concerns, please feel free to click Reply.