This chapter of the guide to Dragon Ball Z: Kakarot has a walkthrough for the Hyperbolic Time Chamber Renovations side quest.
Time frame: From Android Terror Arrives - Episode 10: Intermission to Episode 10: Intermission
Reward: 168,013 EXP, 5x D Medal, Shenron Plush, Card 056
Where to start: Kami's Lookout Area, as Gohan.
Go to Kami's Lookout.
Your mission is to get two red and two green crystals. If you already have them in your inventory, you can give the items to Dende.
To get Phantom Sand, you need to head to Olive Village and then get to the place indicated on the map.
When you pick up Phantom Sand, you will be attacked by opponents. You can't avoid this battle. Win the battle and go back to the quest giver.