Can you delete old bank registers and not one by one

You don't actually "Delete" them unless they have no entries.  You're basically just hiding the Bank Accounts (or any other Acct).  If you created an Account by mistake and have not put any transactions in it, then yes, you are able to Delete that Account.

As for Hiding multiple Accts at once, you can do this in the Desktop version, so possibly in QBO as well.  Open your Chart of Accounts and then click on the Gear Icon and Include Inactive.  You should now see all your Active Accounts and any that you have Hidden/Deleted and are basically "Inactive" Accts.  In QBD there is a column that shows and "X" for the Inactive Accts.  You can add an X to any Account you want to make Inactive.  The other option is to Edit each Acct and select the Make Inactive option there.