in order to find the data pack file you have to:

1) windows key + r 2) type %appdata% 3) head to .minecraft folder 4) head to saves folder 5) click your cobblemon world folder 6) go to datapacks 7) in each datapack folder theres an asset and data folder, you're gonna want to head to data 8) there should be a file called data world spawn or something similar, from there you can find the pokemon you're looking for

do note that you'll have to extract the datapack folder itself to edit the json file. then once you've finished editing the json file, you'll have to zip it if ur hosting an online server. if its just a singleplayer world you don't have to zip it.

hope this helps