improver

/ɪmˈpruːvər/
noun
  1. A person or thing that makes something better or enhances its quality.
    • She is known as an improver of old recipes, adding modern twists.
    • The new software is a great improver of workflow efficiency.
    • This fertilizer acts as a soil improver for gardens.
  2. A person who is learning a skill or trade, especially in a workplace, to become more proficient.
    • The bakery hired an improver to assist the head baker.
    • The apprentice was promoted to improver after six months.
    • He started as an improver in the carpentry workshop.