Rebecca, Welcome to WikiTree.
Do you know where Harry was born, details about his spouse, where he died, things like that? Getting some details about him is a good place to start. We can help if you give us a little more.
Getting an actual DNA match takes a little more work, and there are lots of folks here who will help you with that part.
I am glad you came to G2G, there is usually someone to help you here.