Thank you for dropping by the Community, @smartxs_ltd.
When migrating data from QuickBooks Desktop (QBDT) to QuickBooks Online (QBO), multicurrency transactions aren't supported.
With that being said, yes, you can set up a new Euro bank account and manually fix the transactions that are already migrated.
On the other hand, you can also consider looking for a 3rd party application that'll support migrating multicurrency transactions. As much as I wanted to recommend you but I'm unable to do so as what works for you might not work for some businesses and we treat every business fairly here. However, you don't have to worry since I'll be providing you with this link where you can find one: Apps help QuickBooks run better.
You can type some keywords to maximize the results. This will give you a list of results and you can refer to the customer's feedback and reviews for better recommendation.
Additionally, please know that when migrating from QuickBooks Desktop to QuickBooks Online, your books will appear differently. To know how your books were moved, feel free to browse through this article: Find out how your books will move from QuickBooks Desktop to QuickBooks Online.
Should you have further questions about migrating multicurrency transactions from QBDT to QBO, don't hesitate to include your comments below. I'd be glad to answer them for you and ensure you'll accomplish your QuickBooks-related tasks.
