There's no way to search and easily find how to do the side quest, and it just took me wayy longer than it should have, so here's how to do it for anyone who wants to cheat (like i did):
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before you go to the hot springs, talk to eleni (house closest to the top gate of town), that starts the quest
go talk to clementine, (house under yours). she gives you the pudding.
go to the left side of town and talk to the guy over there by (i think the inn?). big building he's standing outside. he'll play a song for you. talk to him again, and he'll let you borrow his flute.
go to the supermarket, buy 2 bulbs.
you can give the flute and pudding to eleni first, or go to the hot springs now, either is up to you.
after you go to the hot springs, on your way back home there will be 2 light posts with dead bulbs. replace them. now go back to eleni. she'll kick you out for some setup, then go back in. boom. there you go. (this took me like 2 hours.....lol...........)
(edited bc i cant spell :( lol)