Epic Games released an update on Fortnite to add Iron Man's jetpack, called the Stark Industries jetpack, to the battle royale. You will need the v14.40 update to find it though..
There was a jetpack previously in the game, but it was removed in 2018. The Stark Industries jetpack brings this feature back and works like the 2018 original except it has an Iron Man themed skin.
Stark Industries' jetpack would spontaneously appear on the floor of the map. There is no specific location he would arrive in and he does not appear in chests as well..
Keep looking for it until you find it and take your time to enjoy this feature as it is expected to go with the end of the Marvel season. Epic Games has not specified if there will be other jetpacks in the game in the future.
Once you find one, it will take a place in your inventory at the bottom right of your screen. You won't need to select the object to use it, however. Just press the button to jump and hold it to fly. You can also use your weapons while flying with your jetpack..