How to decrease the tactical shooter ai enemy watching range?

in tactical shooter ai the range of the enemy team is too much …they are attacking my hero from a range of more than 1000 meters.but i cant find the solution how can i decrease the enemy’s watching range? please help me out i cant use it in ufps for this problem.

Hi

Enemy Script
Public GameObject Player;
Public float Range;
void Update()
{
Range = Vector3.distance(transform.position, Player.transform.position);

if (Range < 50)
{
//here make your enemy attack the player
}
}