Hi Sara,
If you have only saved the BoE presentation and not completed the transaction, then please try the below steps so that the entries are deleted and then you can present it again.
Execute tcode FBW9 and delete the entries you have created in the last BoE presentation where the Bank is wrong.
Now try to execute tcode FBWE and prepare the BoE again with the correct data and present it.
Please let me know if this works.
Regards
Sree