It's an old saw, but the development of the heavy plough and three-field rotation would be an immense benefit. It always comes up, and at this point I hesitate to even mention it for that very reason, but of course... there's a reason it always comes up. These developments, which showed up together when they appeared in both China and Europe in OTL, were an enormous boon in heavy soil regions. In fact, the OTL development of these things are believed by many (including myself) to have been the key factor in facilitating much more intensive agriculture in Northern Europe. Which in turn led to vastly expanding populations, and eventually to the demographic (and in turn to the eventual political and economic) supremacy of Northern Europe.
The Huns, coming from a non-sedentary background, need a good reason to become fully sedentary early on. Well, the above is just about the best reason one can offer. It doesn't even need any political forethought: the benefits of becoming sedentary and agricultural are self-evident and self-escalating once you've got the right tech to reap such massive benefits. Couple that with the population explosion that will result, and you've got the basis for large population centres, i.e. the growth of cities and eventual urbanisation.
I can think of one motivation - Control.
Philip of Macedon insisted on settle Macedons not just in new cities, but in older ones as well, as it made them easier to control, recruit, etc. Attila or his successors could do the same, but with their various subjects.
As to food, well, the towns will likely figure out a way to adapt, but settlement near the Roman frontier (say on the Danube), and importing food from Rome is a start.
Unlike the Romans however, that motivation for control, gives the motivation to put effort into solving farming problems. The heavy plow isn't a difficult solution, it just needs the motivation. As to the need for the iron to make these in large numbers, the Huns are trying to settle and disarm a large number of former soldiers. Melt their swords.
Plus, they don't even need to invent it - the Chinese already have. If you're seriously looking at settling N.Europe, and you know anything about N.China, just go there, buy one (or the design), bring it back to Europe and copy it.
Sidenote : Honestly, if the Romans had come across a heavy plow or been giving it as part of an agricultural treatise, giving it to the Gauls or Dacians would have caused huuuge butterflies.