How to make code challenge for anyone here to solve?

Answer 1

Make a community post describing the challenge and post it in your feed.
You can also invite some of the members in your post, to participate, by mentioning them.

P.S. don't post your homework as a challenge.

Answer 2

Follow the instructions here.
It is followed by many dedicated problem solvers.
https://www.sololearn.com/Discuss/1270852/?ref=app