Using iphone

How to factory reset your iPhone, iPad, or iPod touch - Apple Support

If this does not work, you will need a Mac or PC to Restore the phone to factory settings. If you don't have one of these products, perhaps you have a friend who would let you use their computer for 20-30 minutes. Most libraries have computers as well. If you have an Apple Store in your area, you can use one of the Macs there. Best Buy has both Macs and PCs as well.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Restore your iPhone, iPad, or iPod touch in iTunes on PC - Apple Support

You don't need a computer to reset, but you would need it for certain types of recovery such as a corrupted iOS installation.