I'd just breed it for better Nature. Though, to an extent, that would depend on whether it's male or female. If it's male, you're pretty hosed until you can get a Ditto, which are of too high a level for you to catch until after you beat the first 3 gyms. You'd also need the water upgrade for the Rotom-Bike to reach the correct part of the Wild Area, outside of Rare raids in that one Den.