Remove encryption from library

I have a seafile 6 server and several large (>2tb) libraries which are encrypted. I’d like to remove the encryption from a couple of libraries permanently, but can’t find an option to do so. Creating a new library is not feasible, as I don’t have the bandwidth to reupload TBs worth of data again.
How can I remove the encryption?

Create a new lib and copy or move the files via the webinterface. Not sure if this works with encrypted libraries though.