I know the importance of keeping the exchange rates amount accurately in your QuickBooks Online (QBO) account, @jess36. That's why I'm here to guide you on the actions you need to get the latest update about matching transactions to an existing bill in foreign currency.

Currently, there isn't any product investigation created to further check the cause of the incorrect exchange rate amount when matching transactions from the Banking menu. With this, I'd recommend contacting our Customer Care team. They can securely pull up your account, check the cause of the issue, and guide you with a fix. You'll first have to check out our support hours to ensure we can assist you on time. Just visit this article's Support Hours section: QuickBooks Online Support.

In the meantime, you can manually edit the exchange rate of your transactions from your account register in the Chart of Accounts the same as what @howardtm suggested above.

Additionally, I'd recommend checking out this article to learn more about multicurrency: About Multicurrency. It includes related articles about exchange rates and how to manually enter one in QBO to name a few.

Please know that you're always welcome to comment below if you have other concerns or follow-up inquiries about the multicurrency feature in QBO. I'm just around to help. Take care always.