How can I make an existing expense account into a sub-account? In other words, how can I move it under another existing master account?

Hi @kotsinil, I'll help move your account.

You can move an existing expense account into a sub-account by changing the account details. Use the accountant view first to follow the steps outlined below.

1. Go to Accounting.
2. Select Chart of Accounts.
3. Choose the expense account in question.
4. Under ACTION, select the Run report menu.
5. Select Edit.
6. Put a checkmark on the Is sub-account selection.
7. Choose a master account from the list.
8. Click Save and Close.

I've included this reference that'll help you understand your account and its transaction history which breaks down how much money you have or owe: The Chart of Accounts in QuickBooks.

Let me know in the comments below using the Reply button if you've got questions other than changing an account detail. I'll be here ready to lead a helping hand. Take care always!

That solved it - thank you.  It should be a bit easier to do this; hopefully intuit will consider that kind of update.