Open Banking Portal is a Self Service for Association members. You can use the Self Service feature to delete your account. Common sense of data modelling suggests that only those accounts can be deleted where the member does not have any active E Lease.
To Delete, please head over to the https://www.open-bank.org/account/ and Press Delete Account.
Even if you are logged in, the platform will ask for your password and upon providing your password and 2 FA(if active), your account will get deleted from the storage.
You should receive an email as below, announcing an account deletion.
In case, if you do not see the option 'Delete Account', it is because, yours is a Verified Account, and one or more E Lease are activated on your account. Read more in Privacy Settings.