how do i do a hard reset of my iphone 8?

Specifically for an iPhone 8, follow these steps:

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the button.

More details and an illustration can be found here.

Hope this helps.

Find out how here: https://www.wikihow.com/Hard-Reset-an-iPhone