I don't think you can downgrade an app that way.
No, you cannot, but I suggested he do that to see if it solved his crashing problems. The vast majority of crash-on-launch issues are due to either:
* Corrupt saved state data (which can be cleared in the Task Manager by swiping the app away, which also shuts the application down if it is still running but it almost certainly isn't unless it is playing audio or doing GPS in the background)
* Corrupted installation. This happens sometimes when you update to new versions of iOS, particularly if you have to do a wipe and restore from backup. To fix this, the simplest method is to just delete and re-download the app.
It has happened to me
with JRemote before, so it was worth trying since the new built seems to fix it for most users.