How can I leave a challenge?

I accidentally joined the first 1000 words Hebrew challenge. How can I leave? I don’t see a button to leave near my avatar, and I already have almost 4k known words in Hebrew.

You can’t leave the 1000 word challenge. You can leave other challenges, but not the 1000 word challenge.
If you already have more than 1000 Known words, the challenge will be considered completed once you make another 1000 words known after joining the challenge.