He will not be able to do that if the transaction is not supporting replace-by-fee. Unless he tries to look for node that is supporting full RBF. I have not done this before and I do not know how it works because all my transaction are supporting replace-by-fee.
I haven't done it myself personally but if OP has the private keys then he can import it to electrum and can reboradcast the transaction with a new signature if he is able to succeed at finding a node that enabled full RBF feature.
Here is how it should be done explained by @hosseinimr93
For making the replacement transaction, you can also use electrum.
- Create a new wallet using your private key.
- Let your wallet get synced and then disconnect your computer from the internet.
- Go to "console" tab and use this command to remove the transaction you want to be replaced from your wallet: wallet.adb.remove_transaction("TXID")
- Close electrum and open it again.
- Make the replacement transaction and export the raw transaction.
Now you have the singed raw transaction and you can broadcast it.
The problem now is that for broadcasting the replacement transaction, you need a node that has enabled full RBF. So, you should try different transaction broadcasting tools until you find a one allowing you to do so and doesn't reject your transaction.