As immmr is still in Beta, please download the app via Hockeyapp. See steps below.
Tap the Download button above on your mobile device. Tap Ok to allow file download and Open once download is complete.
If a popup appears saying Install Blocked, go to Settings > Unknown Sources > Allow installation from unknown sources.
Allow permissions and tap Install. Once installed, tap Open. Register…and start to #SayItWithimmmr.