Assuming you have found a trustworthy source for a "Pokémon Y Randomizer Citra Repack" (usually a .7z or .zip file), here is the installation process.
Even with a repack, Pokémon Y is fragile on Citra. Here are the top 3 issues and fixes: pokemon y randomizer rom download citra repack
If you are downloading a randomizer repack, you are likely a hardcore player. Here is the optimal settings list for maximum difficulty (if you ever patch your own): Assuming you have found a trustworthy source for
We have to address the elephant in the room. Downloading a "Pokemon Y Randomizer ROM" exists in a legal gray area. pokemon y randomizer rom download citra repack