To add the Travel cert to the hse Covidtracker app.
In your device update hse app to latest version.
An additional tab is now on the home page of the App called "View EU digital Covid certificate"
Most have received the pdf hard copy of the certificate, display this (The QR code) on another device, laptop screen another phone ect.
Use the new section on the Covid app to scan the QR code and the certificate is automatically added into the Covid app.
Alternatively is you don't want to use the HSE app you can use another from the app store called Green Pass which doesn't have the track and trace functionality of the hse Covidtracker system.
Also you can just print it out and just include the hard copy with your other travel docs.