How do you fix the home button it stopped working on my phone

You have three options:

1. A ‘cheat’ home button that connects via bluetooth, which doesn’t have touch ID. There is a good video on installing it here
2. Taking it to an authorised service provider to replace it. This is because in the iPhone 7 and above, the home button is paired with the security chip. Only apple has the tools to pair a new one.
3. Jailbreak your phone and add the iPhone X interface to it, which doesn’t require a home button.