James, Wikitree isn't really the place for you to search for 'close relatives' via DNA. You need to upload results to Gedmatch.com (free to do so). This is assuming you've taken an autosomal DNA test. If it's just Y-DNA or mtDNA, then you would look for matches on the site where you had the testing done (e.g. FTDNA, 23andMe or ancestry.com).
Wikitree comes into play when you and others that descend from common ancestors have entered your test kit information on here, and then you'll both show up on the profiles of the common ancestors. At that point, you can compare DNA (not on Wikitree, though, but on the testing site or Gedmatch as previously mentioned).