Changing transaction type in QuickBooks is unavailable, FYGH. However, modifying the Category Account in your expense transactions to Accounts Payable (AP) account will allow you to link them to your bill payments.
I'll guide you how:
Then, here's how to add the expense to bill payment.
Here are some articles that'll help you in handling vendor balances in QuickBooks Online:
Additionally, I've added an article about creating a refund from a vendor. This helps you ensure that all the transactions are recorded accurately: Enter A Refund.
Please get in touch with us again if you need help in managing your transactions in QuickBooks. This way, we'll be able to further assist you.