If you are filling the form on behalf of someone, i.e. client, daughter, father then you are an agent on behalf of that person. If you are filling out the form for your business then you are both the agent and sole trader. Simply place the same details in the fields.
List names clearly in order of preference. Please note if you do not list it in preference, the penalty to refile will be invoiced. T&T has a seemingly high fail rate on names, it's recommended to place about 2-3 options.