If your phone is JB, then using Putty or some other terminal application, SSH into your iPhone as root, then do the following (do not type any double quote symbols, commands and directory names/paths are case-sensitive):
1) Type "cd /var/mobile"
2) Type "ls -la Application"
If you get "No such file or directory" error message when you run the command in #2, then proceed to #3--otherwise I'm not quite sure why you can't get Garmin to work on your iPhone.
3) Type "ln -s Containers/Bundle/Application Application"
4) Type "exit" to close your terminal session
Note: if you "cd /var/mobile/Containers/Data/Application/<ID of Garmin app>/Library", once there you would have "sdcard/Garmin" directory where IIRC you should be able to stick your IMG maps (this is where I store my 3D and DEM maps but I believe you can store your main map here too); here is also where you can create JCV and SID directories for your JCV and SID files. In the "sdcard" directory you can create a new directory named "Vehicle"--this is where you would store your custom/third-party SRF vehicle files.
If after all that it still doesn't work--well I can't speak for iOS 9.3.3 but I have Garmin 2.2 working fine (well, not 100%--it crashes sometimes on Traffic but I reckon it's because Garmin 2.2 is a very old app probably not optimized for newer iOSes) on iOS 9.0.2