The same crash or a different one?
The button to download purchased games is at the top of the page on itch.
An easy way to handle this that doesn't require waiting for me to get the fix out or edit save files, is to load the Steam demo, then quit and go back to the itch version.
It's a script that affects migrating old save data, that had a last minute addition specifically for the Steam version that shouldn't have been enabled for the Itch version.