how do i restore my device

Hi. See these articles:

Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support

How to erase your iOS device and then set it up as a new device or restore it from backups - Apple Support

But what if you don't have a computer to use iTunes to restore? Is there another option?

the computer of a friend and or family or public library would do

it's not possible without any sort of computer assistance