I guess he changed the pw too. the original is not working

Thank you for your help. No, this was a Christmas gift to him and I guess I should have set myself up with a pw he doesn't know and then set him up. So what do I now?

my son who is 7 somehow changed his username in windows10 from his name to a misspelling of his name. Now we can't get into the laptop at all. Any help would be greatly appreciated!