Successfully completed personal challenges are saved on the user's page ("My Profile") in the form of badges indicating the achieved goals, and the user receives bonus charges ⚡️ that go both to the personal credit and to the global challenge score.
To find "Individual challenges" in the app: scroll the main menu down to "Challenges" section → find widgets of several personal challenges in the "Recommended" list → choose the one you like and click "Join the challenge".