Our accountant asked for all information from 2020 to be deleted from our Bank accounts and credit cards can Quickbooks delete these ?

You can use a deleter tool

https://get.transactionpro.com/qbo

Use a backup restore app to lower any risks.

https://partnerwithus.rewind.com/quickbooks

He valhallacsl. Just to add to the valuable info that Fiat has shared above, you can also manually delete the transactions within QuickBooks. 

Here's how you can delete the transactions: 

1. Navigate to the Banking menu.
2. Click on the For Review tab.
3. Select the checkbox of the transactions to exclude.
4. Hit Exclude.

Excluding the transactions will remove them from your QuickBooks bank feed into the For Review page. From here you have the choice to permanently delete the transactions from the For Review page as well. I encourage you to try this and let me know how you make out. I'll be a message away in case you need anything else.