How can I check if the harness is installed correctly?

“Make sure the gap between the harness straps and your child can fit no more than one adult-sized finger. If your child can freely escape the car seat, the harness straps are too loose and must be tightened. Avoid dressing your child in loose-fitting clothing, as this may prevent the harness from being tight enough for your child’s safety.
Always lay harness straps flat. Do not cross, knot, twist, or tie straps together.”