This chapter of the guide to Dragon Ball Z: Kakarot has a walkthrough for The Meaning of Training side quest.
Time frame: From Android Terror Arrives - Episode 2: A Frustrated Vegeta to Episode 3: Driver's License Lunacy
Reward: 46,993 EXP, 3x D Medal, Card 038, Super Sacred Text of Martial Arts
Where to start: Western Area, as Vegeta.
Talk with Tien to start the mission. Your task is to defeat the opponent.
The only thing you have to do in this substory is to win the fight. The enemy shouldn't be a problem for you. Simply use a few good combos to complete the mission.