This chapter of the guide to Dragon Ball Z Kakarot has a walkthrough for Gentle Giant side quest.
Time frame: From Attack of the Saiyans - Episode 2: Rumble with Raditz to Episode 2: Rumble with Raditz
Reward: 86 EXP, D Medal, Silk Apron, Fancy Urn
Where to start: East Ravine Area, as Goku.
In the mountains, you will meet Android Eight known from the original Dragon Ball. You are asked to destroy the Red Ribbon robots. You have to defeat three robots. Enemies are very weak and won't cause you any problems. Go back to the Android to finish the task. You will also get Android Eight's Soul Emblem.