You know your mass is 62kg but when you stand on a bathroom scale in an elevator it says your mass is 77kg what is the acceleration of the elevator

The bathroom scales showing a mass of 77 kg implies that 770 N of force is being applied on it.

620 N of that is by the virtue of weight of the man. The rest 150 N of force which amounts to an extra 150 (62) = 2.4 m/s^2 of acceleration is being provided by the lift.

Since the man is applying more force than on the floor of the lift than he normally would have, we know the lift is accelerating upwards.

The acceleration of the lift = 2.4 m/s^2 upwards