To find the Fortbyte number 49 of the decryption challenge you have to look in Trog's ice cave. Trog is the yeti skin of season 7 of Fortnite and is hidden southwest of Polar Peak. You can reach it by going quite southeast of the map and finding one of the two entrances: find a hole in the ground in the middle of the firs and drop into it or walk along the side until you find the main entrance to the cave.
Once inside the cave, the flea awaits you in Trog's wooden hut and if you are lucky, a hoverboard will have appeared on the hut allowing you to leave quickly.
Written by Augustin "TheGreatReview" Héliot. Translated from French by Millenium.us.org