The challenge applies to certain tiers selected at the end of the month and the rules suggest that you must make an alt with the letters oml in it somewhere and start laddering from scratch following the specific rules given for that month. Also, being number one on the ladder has nothing to do with the challenge, you just need to be higher than the other players that month to win that month, in fact the rules even say not to update your ladder ranking here.
With all that out of the way, you have topped the hidden type ladder which doesn't even matter this month. The challenge this month is actually for balanced hackmons, so if you want to participate in the challenge this month i suggest you give the op a good read and enter yourself into the tournament as per the instructions given.
edit- tbk ninjad me, this was in response to jernmax's comment