What do I do if I find a passport I'd reported lost/stolen?
Never travel on your passport if it has been reported lost or stolen. You run the risk of being stopped at border crossings, as Interpol keeps a record of all reports of lost or stolen passports.
You should return the passport to the Embassy of Ireland at:
The Embassy of Ireland,
541 Orchard Road,
Liat Towers, 8th Floor,