How to resync previously ignored files?

I use a seafile-ignore.txt file in the root of my library to exclude some files from replicating. It works fine.

I now decided to remove one directory from that file so that it synchronizes. The problem is that it does not want to be “forgotten as an excluded item” – it does not synchronize.

How to force a refresh of the excluded files? Or alternatively, force that one directory to now synchronize?