To unlock Scarlett (Zombie Character) in Black Ops 4 Blackout, you need to find the “Racing Goggles & Scarf ” get a vehicle elimination and finish the match in any place. If you fail to complete the character mission for any reason in one match, you need to find the Racing Goggles & Scarf again in the next game again.
The Racing Goggles & Scarf mission item can drop from zombies.
HOW TO FIND ZOMBIES FOR SCARLETT
Zombies always spawn near the mystery boxes around the map. These can be spotted very easy by looking for the blue beams in the sky. Simply keep farming zombies until the Racing Goggles & Scarf drop.
To get the vehicle elimination, find a truck which is a lot safer than the quads. It will take a lot of luck to find the right player in the right situation but if you keep speeding through the map you will surprise a player sooner or later.