working on an endless runner. Need help with clamping.

Hello,

Your question is a little ambiguous, so I've made two examples:

First, this will clamp the user input to be no more or less than 7 or -7 respectively:

 private float edges = 7f;
 public GameObject player;
 public float movespeed = 10f;
 
 private void Update() {
     if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Moved) {
         //Vector3 change = player.transform.position;
 
         Vector3 position = Input.GetTouch(0).position;
         double halfscreen = Screen.width / 2;
         Vector3 clamp = Input.GetTouch(0).position;
         clamp.x -= halfScreen;
         clamp.x = Mathf.Clamp(clamp.x, -edges, edges);
 
         if (clamp.x < halfscreen) {
             player.transform.Translate(Vector3.left * movespeed * Time.deltaTime);
         } else if (clamp.x > halfscreen) {
             player.transform.Translate(Vector3.right * movespeed * Time.deltaTime);
         }
     }

This will still allow your player to move out of bounds however.

If your goal is to keep the player's position within 7 and -7 units on the x axis, try this instead:

 private float edges = 7f;
 public GameObject player;
 public float movespeed = 10f;
 
 private void Update() {
     if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Moved) {
         //Vector3 change = player.transform.position;
 
         Vector3 position = Input.GetTouch(0).position;
         double halfscreen = Screen.width / 2;
 
         if (position.x < halfscreen) {
             player.transform.Translate(Vector3.left * movespeed * Time.deltaTime);
         } else if (position.x > halfscreen) {
             player.transform.Translate(Vector3.right * movespeed * Time.deltaTime);
         }
 
         Vector3 playerPos = player.transform.position;
         playerPos.x = Mathf.Clamp(playerPos.x, -edges, edges);
         player.transform.position = playerPos;
     }
 }

Cheers and good luck!