If Peridot is available to download in your country/region, you can find it in the App Store/Google Play Store on your device. 

App Store (iOS)

https://apps.apple.com/us/app/peridot/id6445801028

https://play.google.com/store/apps/details?id=com.nianticlabs.peridot

Please note that the App Store/Google Play Store must be set to your country/region when checking for availability.