Making knockback smooth instant of instant

I am working on a simple melee attack mechanic but I noticed that no matter what speed I set the knockback to, it always seems like the character just instantly moves back instead of smoothly doing it. Is there a way to make it so I can keep the speed in which the knockback is applied but see the character "slide" back instead of teleporting back? Here is the code I'm using:

  public class meleeAttack : MonoBehaviour
  {
      int speed = 1000; 
 
 
      void Start()
      {
 
      }
 
      void Update()
      {
 
      }
 
      void OnTriggerStay(Collider other)
      {
          if (other.gameObject.tag == "Player" && Input.GetKeyUp(KeyCode.F))
          {
 
              other.GetComponent<Rigidbody>().AddForce(transform.forward * speed);
          }
      }
 
 
  }