hello

If you can still get into settings then,

Settings, General, Transfer or reset iphone, Erase all content and settings.

If you cannot get into settings then DFU it, ie

If you can't update or restore your iPhone or iPod touch – Apple Support (UK)

Naturally take a backup first if you want the data back

How to back up your iPhone, iPad, and iPod touch - Apple Support

Are you trying to restore it yo factory settings, or to restore a backup to the phone?

What error messages do you see?