The NC GOP site covers this process well.

To open a printable Voter Registration Application click on the word “Form” in the yellow or pink section of this page.

The Harnett Voter Registration office is located at 817 S. 8th Street
Lillington, NC 27546.
Their mailing address is PO Box 356, Lillington, NC 27546.
Their telephone number is 910-893-7553, Fax: 910-893-4655.