Make value change to anoter over time and back loop

You can use Mathf.PingPong() or Mathf.Sin() in Update():

 var val = Mathf.PingPong(Time.time * speed, 2.0) - 1.0;

or:

 var val = Mathf.Sin(time.time * speed);

Mathf.Sin() will give a sinusoidal change between -1.0 and 1.0;

The way I do this is the following (taken from a Pac Man game I'm working on where the sprites cycle in a back-and-forth munching loop):

     // Set animation frame
     const int NUM_FRAMES = 4; // In our Pac Man animation, we have 4 frames.  
                               //We want the frames to go 0,1,2,3,2,1 and repeat.
     const float ANIM_SPEED = 0.4f; // Modify this parameter to determine the speed at which the frames progress
     
     int frame = ((int) (this.transform.x * ANIM_SPEED)) % NUM_FRAMES;
     
     if (frame > NUM_FRAMES * 0.5)
         frame = NUM_FRAMES - frame;

     // "frame" will now cycle from 0 to 3 and back again in reverse according to the "x" of the transform.

Edit: So in your case, you have 4 desired values. -1, 0, 1, 0, then repeat. For that, you can do:

     int counter = 0;

     void Update() {
         counter++; // I assume this is going up in some fashion
         int ticktock = (counter % 4); // ticktock is now 0 to 3
         if (ticktock > 2)
             ticktock = 1;        // ticktock is now 0 to 2
         ticktock--;            //ticktock is now -1 to 1
     }

Another way is to use an array to store the values you want to toggle through. This is perhaps one of the easier ways to understand:

     int counter = 0;

     void Update() {
         const int[] values = {-1, 0, 1, -1}
         int ticktock = values[(counter++) % 4];
         // ticktock is now at the desired value
     }

Wait stuff is different depending on are you using c# or unity script.

 int a = 1;
 
 for(;;){
 //infinite loop
 // if unity script use yield waitforseconds any function, if c#create new IEnumerator function, copy the for loop the 
 //re because only in that function you can use yield waiforsecobds
 
 //start coroutine from start or whatever
 
 a *= -1; 
 }