On top of upgrading your characters the Frogs are often used in Genshin Impact, while not that hard to find you'll still need a lot of them so here's a guide to where you can get your hands on a bunch.
Frog Location Genshin Impact
If you're looking for a more precise location for all these Cecillia I'd advice checking the official interactive map where you'll be able to zoon as you see fit.
You can find the map on the Hoyolab website here.
