To start this sidequest, you have to have calmed Divine Beast Vah Medoh.
Speak to Amali, a Rito standing on the bridge that links Akh Va’quot Shrine and Rito Village. She can’t find her daughter, Kheel. She thinks that Kheel is at Warbler’s Nest, which isn’t too far from here, so let’s help her out.
Paraglide west in the direction she indicated. On the minimap you will see the standard footpath going around the lake and then you will see that it branches off to a dead end. That is where the Warbler’s Nest is. As you get closer, you will see a few stone columns surrounding a suspicious pedestal.
Speak with Kheel, the little purple Rito, and it seems that none of her sisters showed up for a planned rehearsal. This will start a new Shrine Quest, “Recital at Warbler’s Nest”. You can learn how to complete this Shrine Quest here.
Return to Amali and tell her about Kheel. In return, she will give you a purple Rupee worth 50 Rupees.