To connect a transmitter to the iOS version of VelociDrone using ELRS you need to use the wi-fi joystick functionality that is part of ELRS 3.4.
At the time of writing this article there was no ELRS 3.4 release candidate - so to build ELRS 3.4 you needed to build the ELRS 3.4 master branch as below.
There are now ELRS 3.4 release candidates so you can just use those now rather than building from the master branch.
Once you have built ELRS 3.4 master branch and installed it to your module you ELRS module will have wi-fi joystick capability.
This video explains the concept ...
https://youtu.be/dJE4O4MkH8Q?si=Kbyyjzq4KQPE8U_q
Once you have everything correctly configured ....
1) ELRS 3.4 master branch installed on your module
2) ELRS wifi setup to connect to your chosen 2.4G wi-fi network
3) Your phone or tablet connected to your chosen 2.4G wi-fi network
4) wi-fi joystick turned on in the game option in velocidrone
5) wi-fi started on your ELRS 3.4 module and the little spinning / (slash sign) showing on your transmitter that wi-fi is running
Note: if you are using a hotspot (recommended) as the wifi network you must have "maximize compatability" turned on for the hotspot as this will make it run as a 2.4G network, with this off the hotspot will be 5G and ELRS will not be able to connect to it.
You can start VelociDrone on the tablet or phone and it should automatically detect your transmitter and you can then run assign sticks in the input menu to setup the controller.