Move the line renderer in a circle with only left and right arrow keys

I am trying to move the line renderer (as an aim) in a circle with only left and right arrow keys but I have difficulties with it. Here is the image of how my game looks.

and here is my script (not completed)

 public class aiming: MonoBehaviour
 {
     LineRenderer lr;
     float input;
 
 
     void Start()
     {
         lr = GetComponent<LineRenderer>();
 
     }
 
     private void FixedUpdate()
     {
 
       // move the line renderer at index 1 depending on the input value
 
     }
 
     void Update()
     {
 
         input = Input.GetAxisRaw("Horizontal");
         
     }
 }