ChangeMin.cs

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

public class ChangeMin : MonoBehaviour
{

    public static float plus = Ui.motiv;

    public void changeMinus(string word)
    {
        plus = Ui.difficulty;
        plus--;

        if (plus < 0)
        {
            plus = 0;
        }

        Ui.difficulty = plus;
    }
}