There are lots of quests to complete in the first week of Chapter 3 Season 1 in Fortnite. After you have discovered the Device, and have a way to communicate with the Seven, you will need to find the Launchpad.
The Launchpad is actually located in a small group of islands out to the east of Sanctuary. Here, on the largest of the islands, you can find the Launchpad area. It will have multiple silos on it, and some small buildings to the west and north.
When you arrive, a message will automatically start playing from the Scientist, and he will ask you to track down and destroy some Signal Jammers. The Seven needs to be able to use the Launchpad, and the Signal Jammers are preventing that.
You can find all three of them at different points on the island, marked on the map above. The first is located behind the building to the north of the silos. The second is beside the building on the very southeast of the island, up the small hill.
The finally Signal Jammer can be found on the beach near the dock to the south of the island. It should only take one blow from your harvesting tool to destroy each one, and that will wrap up the quest.