You can wet-steam block Kureyon. I’ve done it plenty of times.
Simply lay out your piece on your ironing board/iron proof surface. Set your iron to wool or high setting. Either use the steam function of your iron or simply spritz your piece with water. Iron flat. The piece won’t be bone dry once you’re done ironing it flat but it ought to be relatively dry. Let it finish airdrying for a little while.
This saves you from soaking it, pinning and and waiting for it to air dry.
If the pieces still kinda curl, I just take a couple of stitch holders or large safety pins and pin the pieces that are to be seamed together. I pin them a few row under the edge so that the edges are held together, making it easier for me to seam them.