Locked back gate what to do .....?

ok, im required to mow the lawn in my lease , i just moved . but there is a lock on the back gate to were i cant get back there to mow the grass. i informed the landlord but havent heard back from her. should i just remove the whole latch the lock is on and then replace it with a new lock or what. i dont want her or myself to get in trouble with the city if the grass gets too high. and if that should happen with the city would i be liable if they have to mow it and charge the landlord ?