The Parking Brake on the Compass is the small lever attached to the brake lever itself on the handlebar. While squeezing the brake lever, you want to push this lever inward, then release the main lever to lock the brake. To release - you squeeze the main lever, and pull the small lever back.
If the brake is too hard to engage, or isn’t engaging enough - follow the procedure for a Mechanical Disc Brake adjustment, or visit your local Bicycle Shop and have them adjust it for you.