How do i change the AP account for a bill already entered in QB online version?

I'd be glad to join you here and help with your question about using multiple A/P accounts, susana-1si-org.

QBO uses the default A/R and A/P accounts when creating invoices and bills. These accounts are  the ones that were created when you set up your company in QuickBooks Online.

Although, you can create a journal entry when moving balances from one A/P account to another. Here's how:

1. Click the + New button and select Journal Entry.
2. Select the original or default A/P account in the Account column, then enter the amount in the Debits column.
3. Look or the second A/P account in the second line and enter the amount in the Credits column.
4. Enter all details such as date, name of the vendor, and transaction number.
5. Click Save and close.

You can see more details about this process here: Create a journal entry in QuickBooks Online.

For additional references about A/P and vendors balances, allow me to share these articles with you:

• How to Group Accounts Receivable or Accounts Payable Account Types 
• How to Enter Outstanding Balances for Customers and Vendors 

You can always circle back to us if you ever have more questions. The Community is always here to offer or help all the time.  

Hi susana-1si-org,

Hope you’re doing great. I wanted to see how everything is going about using the second A/P accounts. Was it resolved? Do you need any additional help or clarification? If you do, just let me know. I’d be happy to help you at anytime.

Looking forward to your reply. Have a pleasant day ahead!