>>55567647you first need to find a mon with natural non-hidden regenerator, and they are rather uncommon. unless you're in unova.
this can be a fun story, actually- trainer finds and catches a maimed kirlia and makes restoring her to full body the mission of his adventure. they travel the region, then across regions in search of a mon with a suitable ability, in the meantime they get a ragtag team of mons with other useful abilities for her to trace (finding a levitator would be first priority, bonus points for misdreavus, they'd have a fun dynamic with how similar they are), she becomes his ace, evolves, learns to live with that body, to the point where both her and her trainer get kinda sad when they do find a random audino, as it signals the end of the journey, as well as the end of her uniqueness. she'd become just another gardevoir if she battles that audino, with the memories of the adventure as the sole reminder of it.
in the end it doesn't work anyway because if regenerator worked then any other way of healing would have too. 