learn (something) by heart

暗記する、しっかり覚える(根づかせる感じ）

Ex

• I’ll learn it by heart.
• I know this song by heart.

Reference source

• http://press.share-wis.com/learn-by-heart
• https://hapaeikaiwa.com/2013/02/06/learnknow-something-by-heart/