Hi there, @useranneli.
Thanks for sharing your concern in the QuickBooks Community page.
You can find the remaining balance of the partial payment by knowing first which customer has made the payment.
I'd recommend reaching out to them to know which invoices the payment is linked to. That way, you can categorise it in the Banking page.
For more details, you check out how to review downloaded bank and credit card transactions in QuickBooks Online (QBO).
The Community always has your back, so please let me know if you have any other questions. I'll be more than happy to help. Keep safe.