As stated by the developers, 14 challenges will need to be completed over the course of two weeks, with a new challenge being revealed every day at 14 p.m.
Thus, to achieve day 10 challenge, players will have to light different fireworks, on the occasion of the American National Day. These fireworks can be found in several places along the river that divides the island in two, from Lazy Lagoon to the snowy area, as shown on the map below.
When the challenge is validated, it will then be necessary to go to the Challenges tab then 14 days of summer and tap on the corresponding line to unlock the rare gathering tool "Spatula and Fork".
