This chapter of the guide to Dragon Ball Z: Kakarot has a walkthrough for the Anxious Android side quest.
Time frame: From Majin Buu Reborn - Episode 1: Good News to Episode 1: Getting Ready for Son Goku
Reward: 206,721 EXP, D Medal, Super Deluxe Meat Course Recipe, High-Quality Milk, Ripe Peach, Ripe Apple
Where to start: Southeast Islands Area, as Gohan.
To start this mission, you need to go to Kame House. Android 18 is waiting for you - talk to her to start this substory.
Your objective is to get - 3 Frozen Rabbit Meat, 3 High-Quality Onions and 12 River Shrimps. The fastest way to get all the items is to buy them from a merchant.
However, you should have most of them in the inventory.
If you want to collect items yourself, go to the river, farms, and frozen locations. There you will find all the ingredients.
Give Android 18 all the required items to complete the mission.