Erasing my iPhone XS completely

The only difference between the two methods suggested by Michael Black is that, if you choose the latter, you install also a fresh copy of latest IOS during the restore to factory settings procedure:--> Restore your iPhone, iPad, or iPod to factory settings - Apple Support

If you need to give away your device, you can take a look also at this procedure:--> What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Regards

Giulio

Two possible ways. On the device itself you can use the “erase all contents and settings” option in settings, general, reset. Once it erases it will return to the Hello setup screen.

Or connect to iTunes on a computer and select to restore it as a new device. Again, once restored, it will reboot to the Hello setup screen.

BEFORE you do either of those things, sign out with your AppleID from FaceTime, iMessage and iCloud.