Risa is looking for a pokémon that has blue vines on it, which have a nostalgic aroma.
The Request
Go to Jubilife Village and go into Galaxy Hall. Go downstairs and talk to Risa to accept her request.
Show Her the Pokémon
The pokémon that Risa is looking for is Tangela. They can be found in the Gapejaw Bog area of the Crimson Mirelands.
Reward
After you show Risa a Tangela, you will get 5 Smoke Bombs and 2 Exp. Candy S.