How do I set Transform.rotate to an absolute value?

I'm making game that involves a boat, and I'm running into a problem with rotating the boat. When the arrow keys are pressed, I want the boat to turn in that direction to that specific rotation to a definite value, or even better slowly turn to that definite point, and not add to the current rotation. The relevant code that I am currently using is below:

 public float speed;
 
     private Rigidbody rb;
 
     void Start()
     {
         rb = GetComponent<Rigidbody>();
     }
 
     void FixedUpdate()
     {
         //Gets standard WASD and arrow input from player to control the boat
         float moveHorizontal = Input.GetAxis("Horizontal");
         float moveVertical = Input.GetAxis("Vertical");
 
         //Moves boat along x-z plane based on user input
         Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);
         rb.AddForce(movement * speed);
 
         //Rotates the ship based on whether Z or V is being pressed
         if (Input.GetKeyDown(KeyCode.V))
         {
             transform.Rotate(0, 90, 0);
         }
         if (Input.GetKeyDown(KeyCode.Z))
         {
             transform.Rotate(0, -90, 0);
         }
     }

I have also tried:

 GetComponent<Rigidbody>().rotation = Quaternion.Euler(0.0f, GetComponent<Rigidbody>().velocity.x * -tilt, 0.0f);

and:

 GetComponent<Rigidbody>().rotation.y = 90; (Which ran an error).

As of yet I have not found an answer, and whatever I try does not seem to be working. So my question is: what will?