please help me with this.

You can use the "Chance enemy encounter rate" command (or something like that) on the third event commands page and set the encounter to 0. This applies to the whole map as well as the encounter areas.

Not sure how to set it up for random encounters other than what Tiro said, but if they are pre-set I'm guessing they are evented versus being random, so this should be easy enough. Each monster encounter would need to be evented. The first page should have the sprite you wish to use, the commands for battle processing, and whatever happens after that. Then on a separate page, add a switch and call it whatever (Monsters Gone, for example). Leave the graphic blank, and no commands. Each monster event for this area would need the same switch condition. Then create an event that would activate that switch and the monsters should be gone.