Heya! The Sand Town's temple sells herbal tea for this. If it's not available yet, just advance the main storyline further. Though, it should be available at the step you are on.
Viewing post in Yorna: Monster Girl's Secret comments
I eventually found that out. I'm now back tracking to find any kind of secrets that I missed and remembered the geomancer stashes in the first forest with the plants. I'm well into the second island and still haven't found the way to open those. Is the way to open those end game or did I miss something