UI button keyboard input into typing game ,UI button keyboard to input to Typing Game

Hi, i have followed this tutorial How to make a Typing Game in Unity (Livestream) - YouTube . I am a little stuck though, I have followed the tutorial and everything works fine but I would like to use this on a mobile phone so I have made a keyboard out of UI buttons and I’m really struggling to get the buttons to input a letter to the word manager script. I am very new to coding so am probably missing something really simple. can anyone help with this?

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

public class WordManager : MonoBehaviour {

	public List<Word> words;

	public WordSpawner wordSpawner;

	private bool hasActiveWord;
	private Word activeWord;

	public void AddWord ()
	{
		Word word = new Word(WordGenerator.GetRandomWord(), wordSpawner.SpawnWord());
		Debug.Log(word.word);

		words.Add(word);
	}

	public void TypeLetter (char letter)
	{
		if (hasActiveWord)
		{
			if (activeWord.GetNextLetter() == letter)
			{
				activeWord.TypeLetter();
			}
		} else
		{
			foreach(Word word in words)
			{
				if (word.GetNextLetter() == letter)
				{
					activeWord = word;
					hasActiveWord = true;
					word.TypeLetter();
					break;
				}
			}**strong text**
		}

		if (hasActiveWord && activeWord.WordTyped())
		{
			hasActiveWord = false;
			words.Remove(activeWord);
		}
	}

}