If he has online access to his Australian bank account, he could sign up with wise.com and use that to transfer the money from his Australian bank account to his existing Irish bank account. I've used it to transfer money from Ireland to Asia and the exchange rate is very good and the fees are low.
Wise is not a bank account per se. Just a service. He logs into Wise and says that he wants to transfer, say AUD 2,000 to his Irish account and provides Wise with the IBAN/BIC of the Irish account. Wise then gives him a reference number and account details for Wise Australia. He logs into his Australian account and transfers the AUD 2,000 to the Wise Australia account, using the reference number. As it's a local transfer, no exchange rate or mad fees. Wise Australia theoretically transfer the money to Wise Europe (Belgium I believe). And from there it's a Eurozone transfer to his Irish account.
Edit: I would be cautious with Revolut as a main bank account due to the risk of scams.