For the app, just google "Tamagotchi 4U App". The first result should come up with the English translation hosted on Mr Blinky's website. This is much more easier and has more content than the Japanese app.
As for the IR on the 3DS no, even Tamagotchis with IR this will not work. As far as I know not much can access the IR, yet alone sent a file to your 3DS. You can easier buy a IR USB online, cheap as chips. Heck, you can get a Windows 98 computer to send files to your Tamagotchi by IR however, the 4U uses NFC, not IR. One of the first Tamagotchi models to use NFC besides the Tamagotchi Friends. The new 3DS does have NFC, but only enough to send random events (When the 4U reacts to any NFC, it plays an Easter Egg). There is no program to send files to your 4U on the system, so far its only for amiibo.