Set a relative (custom) speed to a rotation

I am making a character rotate around its axis using euler angles. Not quite as transform.Rotate that makes the character fall through the terrain. But I want it to put a custom speed. I mean a float or something that can be edited in the script for the character to rotate at a speed I want to set in the script.

  if (((Input.GetAxis("Horizontal") > deadZone) && !Input.GetKey(KeyCode.LeftShift)) ||
 (Input.GetAxis("Horizontal") < -deadZone) && !Input.GetKey(KeyCode.LeftShift))
 transform.eulerAngles += new Vector3 (0, Input.GetAxis("Horizontal"), 0);

It means that if i press the left or right inputs, the character rotates around its y axis. Now i have to set its speed. How could I set a relative speed to it???

Like this:

     if (((Input.GetAxis("Vertical") > deadZone) && !Input.GetKey(KeyCode.LeftShift)) ||
         (Input.GetAxis("Vertical") < -deadZone && !Input.GetKey(KeyCode.LeftShift)))
         TP_Motor.Instance.MoveVector += new Vector3(0, 0, Input.GetAxis("Vertical"));

This is the other code from the other script:

 public Vector3 MoveVector { get; set; }
 public float VerticalVelocity { get; set; }

 void Awake () 
 {
     Instance = this;
 }
 

 public void UpdateMotor () // Le cambie era UpdateMotor
 {
     ProcessMotion();
 }

 void ProcessMotion()
 {

 // First Movevector

     // Transform MoveVector to worldspace
     MoveVector = transform.TransformDirection(MoveVector);

     // Normalize MoveVector if Magnitude > 1
     if (MoveVector.magnitude > 1)
         MoveVector = Vector3.Normalize(MoveVector);

     // Multiply MoveVector by MoveSpeed
     MoveVector *= MoveSpeed();

     // Reapply VerticalVelocity MoveVector.y
     MoveVector = new Vector3(MoveVector.x, VerticalVelocity, MoveVector.z);

     // Apply Gravity
     ApplyGravity();

     // Move the character into world space
     TP_Controller.CharacterController.Move(MoveVector * Time.deltaTime);
    
 }