@ScriboDT 

"Is there a way to change the asset account to an income account or retroactively correct the old transactions in the asset account?"

Were the payments received using an item on an invoice?  If so, you should be able to update the 'Account' on the item and select the desired income account.  QB will ask you if you want to update existing transactions.  If you select 'Yes', QB will update all historical transactions that used that item.  Be careful if any of the transactions are in previous, closed periods. 

If the other current asset account was assigned to the deposit of the prepayments, then I believe you need to go through and change them one at a time.