Hi Rushabh

The time period of the Bob of a simple pendulum depends on the effective length of the pendulum string, i.e. the length from the point of suspension to the center of mass of the bob.

Hence if the center of mass moves upwards from the initial position, the effective length will decrease and the time period will also decrease.

If the center of mass is lowered, the effective length of string will increase, this increasing the time period of the bob of the pendulum.