In this Week 12 challenge in Fortnite, Doctor Slone will ask you to craft a weapon using alien nanites.
Nanites have several uses in Season 7, such as the ability to transform your weapon into an IO or alien equivalent. This means Nanite becomes a crafting material, just like wood or stone.
Where to find alien nanites in Fortnite
Luckily, Nanites be found absolutely everywhere on the island. You can look directly at the ground, or find them in standard chests. Believer Beach is a good location to look, for example.
To guarantee finding Nanites, you can also opt to board the Mothership or Abductor Saucers. The special chests found on these will contain Nanites.
Once in your possession, you will be able to improve your weapon. Several combinations are possible.
For example, a Rare or higher quality submachine gun will net you a Kymera Pistolaser, while upgrading a Rare or higher quality assault rifle will get you the Pulse Rifle. For the heavy duty railgun, you'll need to upgrade a sniper rifle of Rare or higher quality.
The most complicated part of this challenge is finding a weapon of at least rare quality.
Also note that you only need one alien nanite to upgrade the weapon. Open your inventory and then use the crafting interface to complete the challenge.