Contact the testing company and inform them that the person has died. They may require a copy of the death certificate or court documents showing that you are an heir to the estate. They will inform you of the steps you need to take to gain access to the account.
It might also be helpful to read the terms of service before you contact the company, so you know up front what they expect in this regard. Sometimes, if you are the person who purchased the test, that will help to establish your right to have access, now.