Diving is Beauty
Talk to Gruve who is standing by a waterfall. You will need to equip your Zora Armor for this which you can receive in the process of calming Divine Beast Vah Ruta. The second prerequisite is that you have calmed Divine Beast Vah Ruta already. Learn more about this main quest here.
To complete this sidequest, dive down the waterfall into the water below. To dive, simply press [X] to jump. Link will automatically assume the perfect diving position. No need for a running start, but be aware that there will not be an onscreen prompt for you to follow.
Once you have landed in the water, Gruve will tell you that he wants to see you swim back up the waterfall. So do so by pressing [A] once the onscreen prompt appears.
After Paragliding back down to the ground, speak with Gruve again and he will give you 5 Fleet-Lotus Seeds as a reward for showing him a beautiful dive.