To install and test developer version of the application you need to register your device. For that you have to send UDID device identifier to developers of the application. Use following instructions to get UDID identifier:  

Variant 1 (use udid.io service)

  1. Within your iOs device with Safari browser visit http://udid.io
  2. Follow instructions of the service
  3. Send device UDID to the developer of the iOs Application 

Variant 2 (use iTunes)

  1. Follow the instructions presented here: http://whatsmyudid.com (Connect your iPhone to your computer and open iTunes. Select your device in iTunes so you can see the serial number. Click on the serial number. The UDID will take its place. You can copy & paste the UDID that's displayed on the screen) 
  2. Send device UDID to the developer of the iOs Application