I have checked the Play Store page and IMO requires Android 4.0 and up to be installed properly. You will have to upgrade the Android version on your phone to be compatible with the latest changes, and then you should be able to install the application. To do this, charge the phone to at least 85 % and access a WiFi network. You have two ways to update the firmware:
Install KIES on a computer and connect the phone to this PC, then follow the instructions in the KIES application.
While you are connected to a WiFi network, go to Settings > About > Software Update and check for updates.
After you have updated the firmware on your phone, access Play Store and search for IMO, then you will have the possibility to install it.