As you would check the wheels on your car, your Opentrons robot requires service on its wheels as well to maintain optimal performance.
-8mm / 10mm wrench
Take your 8mm/10mm wrench, using the 10mm side, and grasp the "eccentric screw" which is located between the plate and the wheel. Slowly turn your wrench until you feel a slight resistance. To test if the wheel has been tightened enough, grab the wheel with your pointer finger and thumb and attempt to turn the wheel manually. The wheel should be able to shift the robot's axis when you move it back and forth.