amend
悛 centers on changing one's ways for the better: amending faults, reforming behavior, or correcting past wrongs through a shift in heart.
悛 combines 忄 (heart/mind) with 夋, which likely contributes the sound and may relate to the idea of changing or progressing. The exact historical development of 夋 is uncertain.
The heart radical 忄 beside 夋 suggests a change of heart. Picture someone's heart turning away from old habits and stepping onto a new path, amending their ways.
For シュン, imagine a person amending their behavior after a stern shun from their friends: shun -> シュン, and the heart changes to avoid being shunned again.