How to make enemies fall at regular intervals

Hello, we are making a game based on old retro game called pooyan.
It’s basically shooting enemies falling randomly which is very easy.
but the problem is we need to make enemies fall at regular intervals so that if the user shoots specific arrow, then it would fly in an arc and can kill all the enemies at a time.

we have thought of calculating frame but it makes no sense
Here’s what I’ve done and it’s not working…

public class Mouse : MonoBehaviour
{int frame= 0;
int n = Random.Range(1, 6);
// Start is called before the first frame update
void Start()
{
}

// Update is called once per frame
void Update()
{   frame++;
           
    if (frame % (100*n)) = 0)
    { GetComponent<Rigidbody2D>().gravityScale = 1; }

}

Please help us out!

add these lines to a mainGameController and call it from a start or at some point with InvokeRepeating(“YourFuncNameHere”, init delay, Repeat delay)

P.S: check for syntax errors if any.

void Start()
    {
        InvokeRepeating("FallingFunc", 2.0f, 0.3f);
    }

    void FallingFunc()
    {
       //your code here for example adding the gravity line of your's
        someObject.GetComponent<Rigidbody2D>().gravityScale = 1;
    }