You need to wait until the leaf comes back into case, or bring it back into case.
My leaf is hung in my shed until the ambient weather permits me to handle it. Sometimes I will help it along, drape wet cloth around the shed, water the floor, open windows/door at night and close in the day. After the leaf is fully cured and dried, and after a few rainy days or high humidity, and the leaf is in-case, I will de-rib it and lay the leaf-halves in a box, flattening as I go.
The 'box' that I use is made of corroplast (yard signs), just barely taped together. The box is sized so the resultant 'bale' is conveniently sized to fit my kiln shelf. When the box is full, or partially, if I only have a few strings of that strain of tobacco, I drop the box sides and remove the bale to storage. I box each strain seperately, and sometimes each lower, mid or top leaf of a strain.
While de-ribbing the leaf, I lay the leaf halves on the work surface, and smooth or flatten as best as I can - not always possible. If tips are too dry, de-rib as best as I can, just put in the box as is. I place a board over the leaf in the box, and use a little pressure to compact the leaf a bit in the bale. My bales are essentually 'loose', so I can seperate leaf easily later. I don't worry much if the leaf is a bit curly, just do what I can and bale it. Curly or folded leaf can go through the pasta shredder just fine. If some leaf is a bit dry, I de-rib as best I can and throw the broken leaf pieces into the box.
I put a sheet of parchment paper in the bottom of the box, and on top of the finished bale, and string-tie the bales a bit, so it's easier to handle. Yeah, I know, I'm a bit anal !
This is also when I do a final inspection of the leaf - throw out the nasty ones, remove dirt, bird feather, tear off dried-green parts of leaf, whatever. My leaf bales are finished 'product', ready for fermenting, storage or shredding/use.