In forward bias, the p-type is connected with the positive terminal and the n-type is connected with the negative terminal.
With a battery connected this way, the holes in the P-type region and the electrons in the N-type region are pushed toward the junction. This reduces the width of the depletion zone.
The positive potential applied to the P-type material repels the holes, while the negative potential applied to the N-type material repels the electrons.
As electrons and holes are pushed toward the junction, the distance between them decreases.
This lowers the barrier in potential.