Question How will Feebas evolve into Milotic?

If you mean in the catcher, all of the Pokémon that evolve with an item have a mystery level that they evolve at. Just keep training it and it will evolve eventually, as long as the admins didn't forget to set it to evolve.

 

All Pokémon that evolve with unique conditions have a fixed level for when they evolve in the catcher (check out this thread for checking/reporting information like that). For Feebas to Milotic, it's level 40. I know this mostly because I trained a Feebas a while ago, so that level is confirmed. The Catcher Dex also has some other evolution levels listen, but it is currently hidden since it's still being worked on and edited so that it can help everyone better. Be sure to check for it once it's back up!