NPSP How-To Series: Override a Default Contact Address (2:31)

Source: https://www.youtube.com/watch?v=dwqYGEe0y-g&t=0s&list=PLU8xqF8ZASbXWAHIF0SB1P9_3G4vvRMXI&index=4

Use Address Override checkbox in situations where you want to send individual mailing to a Contact at a different address than the default Household Address

Go to the Contact’s record and click on the pencil icon next to their Mailing Address

Change the Primary Address Type
Update the Mailing Address details
Check Address Override to set the new address as the primary address for the Contact

Uncheck Address Override to revert the Contact’s Mailing Address back to the default Household mailing address