I set up a current liability account for car loan, but I forgot to enter loan amount as negative. How do I fix this?

Thank you for reaching out to the Community. It's my priority to help you sort this out, @coolimageusa.  

We can edit the account you've created through Chart of Account. Let me show you how.  

1. On the left pane click Accounting, and choose Chart of Accounts. 
2. Choose the specific account under Action View register drop-down arrow, and choose edit. 
3. From When do you want to start tracking your finances from this account in Quickbooks, drop-down arrow, select the starting date.  
4. Enter the Amount.
5. Click Save and Close. 

Once done, you can check from chart of account and under QuickBooks Balance the amount will show up. 

For additional information on this, I recommend the following article: 

• Set up a loan in QuickBooks Online  

Though, if you wish to record and track the money you load, you can enter either full or partial payment. Here's how: 

1. Click + New. 
2. Choose Journal entry, (Note switch to Accountant view first, to control over like the chart of account). 
3. On the first line, under the Account select the liability account you've created, and enter the amount load in the Credit column. 
4.  On the second line, select the appropriate asset account from the Account dropdown. Enter the same loan amount in the Debits column.

 This will track down the loan you have spend.

If you have any other questions, don’t hesitate to comment below. Have a great day!