How do I make my character cool down?

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C#

so I made this script that heats up when the player moves but I cant figure out a way for him to cool down when he has stopped moving. how should I fix this?

code:

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

public class Temperature : MonoBehaviour
{
public Slider staminaSlider;
public int maxStamina;

public float minTemperature = 32;
public float temperature = 32;
public float maxTemperature = 105;

public float temperatureFactor = 30;
public bool overheating;

[Header("Temperature Settings")]
public float freezingTemp;
public float currentTemp;
public float normalTemp;
public float heatTemp;
public Text tempNumber;
public Image tempBG;


void UpdateTemp()
{
tempNumber.text = currentTemp.ToString("00.0");
}

void Update()
{
float tempChange = Time.deltaTime * temperatureFactor;
if (Input.GetKey(KeyCode.LeftShift) && !overheating)
{
temperature = Math.Min(maxTemperature, temperature + tempChange);
if (temperature == maxTemperature)
{
overheating = true;
}
}
else if (!Input.GetKey(KeyCode.W))
{
temperature = Math.Max(minTemperature, temperature - tempChange);
if (temperature == minTemperature)
{
overheating = false;
}
}

if (currentTemp <= freezingTemp)
{
tempBG.color = Color.blue;
UpdateTemp();
}

else if (currentTemp >= heatTemp - 0.1)
{
tempBG.color = Color.red;
UpdateTemp();
}

else
{
tempBG.color = Color.green;
UpdateTemp();
}

if (staminaSlider.value > 0)
{
currentTemp += Time.deltaTime / 5;
}

else
{
if (currentTemp >= normalTemp)
{
currentTemp -= Time.deltaTime / 10;
}
}
}
}

What I have tried:

asking help on forums but have had no clear answer