How to restore my IPhone to factory settings without a computer?

Your need has been anticipated by Apple→How to factory reset your iPhone, iPad, or iPod touch - Apple Support

Follow the instructions here: What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

If you don't know the Lock Screen passcode and/or the iCloud account signed into the device, that's a different can of worms entirely.

You can reset your phone as follows:

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

If you are intending to “wipe” your old phone of all personal data prior to transfer or disposal, see this:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

To restore an iPhone, see this:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

If all is well......tap Settings > General > Transfer or Reset iPhone > Erase All Content and Settings

If all is not well.....you may need to use a computer.

good morning, Chattanoogan and Bob Timmons; great minds think alike (and at the same time)😏

Good morning guys!

👋