Upon deployment, you'll find yourselves in the sewers leading to the facility. Proceed forward, eliminating the initial few zombies you encounter. These are standard infected; a few headshots will suffice. Use your melee attack if they get too close to conserve ammo. You'll soon reach a locked door requiring a keycard. A short cutscene will play, introducing the concept of security systems.
Locate the nearby console and interact with it to bypass the security. Be aware that this might trigger more zombie spawns. Once the door is open, continue through the corridor. You'll encounter more zombies, including some that are slightly more aggressive. Stick together as a team and focus fire on individual targets to quickly neutralize threats. The path is linear at this point, guiding you directly to the lab entrance.