Hi Sarah
Welcome to the forum and beekeeping.
There’s a post on the forum already where someone in France has modified a Dadant hive to accommodate a Hybrid Flow Super 4 frame on top, here, however, your super is 3 frame which is narrower.
I’m personally not familiar with Dadant hives and the different sizes available. I wonder if there is a smaller version available (i.e. how many frames does it hold) that you could easily modify to suit your 3 frame Hybrid Flow Super. Note that this size super is equivalent to an 8 frame Langstroth hive, Langstroth being the most commonly used hive in the world and what other beekeepers in your region may be more familiar with in terms of size/dimensions, compared to a Flow Hive/box. The Hybrid Flow Super 4 frame (used in the link above) is compatible with the size 10 frame Langstroth box.
Advice from the bee supplier is a great place to start, with the key info that your Flow boxes are the same size as Langstroth 8 frame and depth is full-frame depth.