First of all, you need to connect to the Fygr application:

https://app.fygr.io/signin
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Once you have logged in, go to the "My banks" section:

Click on the red bin associated with the bank you wish to delete:

Confirm the deletion by typing DELETE in the text field provided, then click on the Delete button.

You can then refresh the web page, all the data should now be up to date.