Using Desktop Pro 2019. When trying to change the type of an expense account in order to make it a sub account. Where is the 1099 Preferences that the program refers to?

go to menu Edit > Preferences > scroll down the left panel until you find Tax 1099

I had already gone into edit>preferences>Tax1099 and changed "do you file 1099-misc forms?  to  NO   but when I tried to make one expense account a sub account of another expense account, it would not.  It said: You can't change the "type" of an account that is associated with a 1099 category. You must first delete its association in the 1099 Preferences.  All that can be done in 1099 preferences is what I already did.  Unless there is something that I missed.

I'll guide you to the section where you can make the expense account unassigned from the 1099 accounts,  spurgeon20.

Let's go the 1099 Wizard and change the information. Just make sure the preferences if turned back on so you can see this option. Here's how: 

1. Go to the Vendors menu, select Print/E-file 1099s, and then click 1099 Wizard.
2. Click Get Started.
3. Click Continue twice.
4. Under the Map vendor payment accounts window, look for the expense account.
5. Click the drop-down list under the Apply payments to this 1099 box column and select Omit these payments from 1099. 
6. Click Continue until the last page, then click Save and close.

Once done, go back to your Chart of Accounts and proceed to making the account a sub-account. More details about the 1099 Wizard are discussed here: QuickBooks 1099 Wizard.

In addition, you can run a 1099 summary or detail reports to keep track of the transactions that are already part of your 1099s at the end of the year. Here's an article for more info: How To Create 1099 Summary Or Detail Reports.

Don't hesitate to add a reply if you require further help with your expense accounts and the 1099 Wizard in general.