8th gen iPad I want to go back to the original configuration after quick start
To restore an iPad to factory settings, connect it to a computer running macOS 10.15 or later, or to a PC/Mac running iTunes. It will show up in Finder (or iTunes) from where you can initiate the restore.
Apple has it documented in detail in Restore your iPhone, iPad, or iPod to factory settings.
If all you want is to run the setup assistant, open the settings app and in general, there is a reset all settings option.

Choose “Erase all content and settings”