It took me awhile of testing until I finally figured out how to make it work myself. The arbor has to be piped into the bottom of the reformer. You can either put one warded jar directly underneath and just replace when it runs out or use essentia pipes (what I did) to make the connection.
Also, just an FYI as to how it works. As it says in the book, it does have a radius of 16 blocks, however, what it doesn't mention, is that it chooses a random block to change each time it does its work. It also does work in a square shape (and not a circle like how witchery's circle magic would do it). Just be aware that to do the entire size it is capable of, you will need a LOT more warded jars that what you have there. I believe 16 full jars will do it if my math is correct.
My last point of advice, give it plenty of time to work, its not super quick at it and you can see it work while its doing it. I would also recommend closing the world and reloading when it is done as well. When it finished for me some blocks still showed wasteland so I thought it wasn't done so kept feeding it more arbor, but once I relogged it was perfect. Although, because of this mistake of feeding it more arbor than it needed, I learned that it will keep accepting arbor even when it has nothing to do and when you break it you lose all of that, so you want to be careful to not give it more than it needs.
If you want to make life easier, and not have to lug the warded jars back and forth, you can always connect a couple of pipes to the reformer and then put an essentia pump to the end, and an essentia mirror close by that it can pull from and then the mirror's pair near a warded jar of arbor at your alembic and it'll grab from it constantly. Just be careful of giving it more than it needs like i did
Hope this helps!