Homing Missile. The algorithm is taken from http://www.freeactionscript.com/tag/game-examples/

HomingMissile.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class HomingMissile : MonoBehaviour
{
    [GetComponent] [SerializeField] private Rigidbody2D m_Rigidbody2D;
    public Rigidbody2D Rigidbody2D { get => m_Rigidbody2D; }

    public Transform Target;
    public float Speed = 5;
    public float TurnRate = .7f;
    public bool IsRotating = true;
    public float RotatingOffset = 0; // zero —> sprite head in right side

    private Vector3 m_Move;

    private bool m_HasPhysics;

    private void Start()
    {
        m_HasPhysics = Rigidbody2D != null;
    }

    private void FixedUpdate()
    {
        if (Target != null)
        {
            //get distance between follower and target
            var distance = (Vector2)Target.position - Rigidbody2D.position;

            //get total distance as one number
            var distanceTotal = Mathf.Sqrt(distance.x * distance.x + distance.y * distance.y);

            //calculate how much to move
            Vector3 moveDistance = TurnRate * distance / distanceTotal;

            //increase current speed
            m_Move += moveDistance;

            //get total move distance
            var totalMove = Mathf.Sqrt(m_Move.x * m_Move.x + m_Move.y * m_Move.y);

            //apply easing
            m_Move = Speed * m_Move / totalMove;
        }

        if (IsRotating)
        {
            transform.rotation = Quaternion.Euler(0, 0, 180 * Mathf.Atan2(m_Move.y, m_Move.x) / Mathf.PI + RotatingOffset);
        }

        if (m_HasPhysics)
        {
            Rigidbody2D.velocity = m_Move;
        }
        else
        {
            transform.position = transform.position + m_Move;
        }
    }
}