Welcome to the Community, @Simon-PM.

I want to help you with your concern about importing transactions with foreign currencies in QuickBooks Online (QBO). The currency reflected in Banking will depend on how you set up the Bank in the Chart of Accounts (COA).

Once you have imported this, you can no longer change its Currency. To rectify this matter, I recommend you recreate the account and choose the appropriate Currency. I'll show you how:

1. From the left navigation pane, select the Accounting menu.
2. Select the Chart of Accounts tab, and click the New button.
3. From the Account type, select Bank.
4. In the Save account under section, select Checking.
5.  Enter the details for the Account Name, Description, Starting date and opening balance.
6. Under the Currency, choose the currency from the transactions under that account.
7. Lastly, click Save.
   

Afterward, reconcile your account to ensure that everything is balanced.

If you have more concerns about foreign Currency, you can always tap me here in this forum. I'll get back as soon as I can. Have a good one!