Mary,
The easiest way to have your brother’s DNA Test added to WikiTree is to go to his profile and on the Edit page, add his email address in the box provided. He will get an email invite to join WikiTree as a family member.
Once he is set up as a family member, he can log into WikiTree and go to his profile. At the top of the profile page under “Add”, he selects “DNA test information”. On the page that comes up, he just adds whatever test he took, his profile name for that testing company and in the case of GEDMatch, the GEDMatch ID number. Then he hits the save button at the bottom of the page.
It takes about 24 hours for the test results to migrate upline through the ancestor profiles.