Welcome to the QuickBooks Community, JJ614. Please know that we aim to deliver customer satisfaction at all times that's why we address an issue as soon as possible. With this, may I ask for additional details on which part of QuickBooks did you change the currency? Also, screenshots of how did you perform the issue you're referring to? I appreciate any further details so I can present an accurate solution.

For now, you may refer to this article to see various information on how QuickBooks uses exchange rates and how it works: Learn about exchange rates in QuickBooks Online.

Please don't hesitate to click the Reply button below and add extra info about your concern. I'm only a comment away. Take care and stay safe, JJ614.