What wallets can be used to double spend (low tx fee workaround)?
As I understand if I send a new transaction, with a higher fee, I can reuse the (confirmed) inputs and that transaction will be accepted, then the transaction with the unconfirmed input will be abandoned.


No. It seems to me you are trying to do Replace-by-Fee, which you need same input that is unconfirmed transaction.

I assume that there are two transactions that you want to get confirmations. Can you post these transaction id so that I might be able to help you.