You should be able to just copy and save these two files somewhere secure, and then paste them back after reflashing Crimson:
Chat history:
/home/purism/.purple/chatty/db/chatty-history.db
MMS images and and other media:
/home/purism/.local/share/chatty/mms
There’s no official export or import for Chatty yet.
You can delete what you don’t want to keep before you save those files above, or after you add them in Crimson.
Here’s some additional info you might want to explore: Tutorial: Export call & chat history as .csv