If you need Challenger or Space Lord achievement all you need to do is download this file:

https://drive.google.com/drive/folders/1HXe0DmncL-48YgamZgeebNekszdZonIf?usp=sharing

Its save with Jack character with lvl 49 with just a little more xp for lvl 50
Place it in Documents/My games/Borderlands The Pre-Sequel/WillowGame/SaveData/76561198097633515

In order to get Challenger you need to update challenges list by completing any of challenges you find the easiest
( Over Achiever is pretty easy at this point in the game if you play it on normal mode )

Any thanks to this guy:
https://steamproxy.net/id/BigNoseGreg

Enjoy!