Most of the nodes (and miners) on the network saw your first transaction when you sent it. They added it to their memory pool (a list of unconfirmed transactions that have been seen by a node). Most nodes and miners will refuse to accept a competing transaction that spends the same bitcoins (often called a "double-spend attempt") while the original transaction is still in their memory pool.
Eventually, if the first transaction doesn't get confirmed, they will remove the original transaction to make room for new transactions. Since Bitcoin Core keeps re-broadcasting the transaction, it will remind them about the new transaction once they've forgotten the old one. Then once the new transaction is in the memory pool of some miners (or mining pools) your new transaction will have a chance to confirm.
If the old transaction confirms, then the new transaction will be invalid and will be abandoned and forgotten by the entire network.
If the new transaction confirms, then the old transaction will be invalid and will be abandoned and forgotten by the entire network.
It might take a few days for enough nodes to forget the old transaction so that your new transaction can get to some miners (and mining pools). You have no control over the memory pool of other nodes, all you can do is wait.