The "lab" feature has been added on the 21st December 2018 update.

Players can enter the "lab" by pressing the "Battle > Weapons" "Battle > Outfits" button io your lobby screen and here players can enhance certain gun skins.

Please keep in mind that not all gun skins can be upgraded.
Only certain skins which can be acquired from a paid crate.
Also, normal outfit skins cannot be upgraded and some exclusive outfits can be obtained from a paid crate randomly.