You don't, you get reward based what your current rank is (which, as it stands, is minimal special jonin)
If you are lazy, you can just sit around and let the season reward point carry you back to super kage, then purposely lose a few fights every season and stay at super kage for 90% of the max reward with absolutely no effort required.

Now that you basicly explained it as easy as posslible this system doesnt make any sense. IDK who made it but clearly he was a monkey

To get the full rewards every time, I need to fight my way back to 6 paths sennin?

guys check arena rules
ARENA’s Seasons-
1. In the first day of each month, if you reached Six Paths Sage rank, all your Rank Points will be reset (in order for the player to obtain all the rewards again, including Konohamaru ’s fragments).
2. Players who did not achieve Six Paths Sage rank will not have their Rank Points reset, but they will only obtain the minimum rewards of the Season’s competition. (minimum means ninja school or genin)