What will be the effect if I put the currency of a USD bank account to GBP in Quickbooks Online and it is connected to bank feed?

Thank you for contacting us about connecting a USD bank account, accounts-twilllo.

You'll want to make sure your books have accurate records. That being said, you can disconnect the USD bank account. 

Here’s how to disconnect an account from online banking.

1. Go to the Banking menu or Transactions menu, then select the Banking tab.
2. Select the tile for the bank account.
3. Click the pencil ✎ icon, then select Edit account info.
4. Select the Disconnect this account on save checkbox
5. Click Save and Close.

Once done, make it inactive to hide the bank from the register. Let me guide you through the steps.

1. Go to Settings ⚙ and select Chart of accounts.
2. Find the account you want to delete.
3. Select the Action ▼ drop-down and select Make inactive.

After making the account inactive, set up a new one with the correct currency. Then, connect it again to online banking.

To learn what to do when you connect banks that use foreign currencies, check out this article: Add transactions in a foreign currency. 

Everything you need about foreign entries can be found through this link: Multicurrency and accounts. It includes related topics about the multicurrency feature.

Stay in touch with me if there's anything else I can help you with your bank accounts. Just leave a comment below, and I'll get back to you.