Under Bill function, I found the credit to another code and not for AP. So how shall I change back?

Hi there, julia-zhu.

The A/P account will be credited automatically when creating a bill. QuickBooks Online will post it to the default A/P account. You'll want to check the Chart of Accounts to verify the account type and see if it's renamed.

Also, you'll want to pull up the Journal report to see the debits and credits for each transaction. Simply go to the Reports tab and search it.

I'll be here if you have more questions. Stay safe!