Well known issue
You can use this to go back a save or whoever sent the missing the pokemon
https://www.rebornevo.com/forums/topic/18748-a-guide-to-using-your-backup-saves/
Go back a save
Go to this location on your computer:
C:\Users\Your user\Saved Games\Pokemon Desolation
Find the one called game.rxdata and delete it or move it and call the highest numbered backup Game.rxdata
This is what a backup will look like
1263 - Starry - 151h 47m - 18 badges
In Linux version it was made for Linux which normally doesn't use that type of file from my understanding
There should just be one called game with the Reborn ball symbol that u use from my understanding
It should all be packed so u just double click on it and it plays