You're player must meet the criteria to join the NT. They must be from the certain country to be for that NT (i.e. American players can only be on the USA NT). Having an NT player provides you a bit more Merchandising profits for your team, and gets your team well known and advice on your training.
That's not what the OP is asking.
"National Team Scout" is a title some countries use to make people who help out feel special. Different countries national teams use different techniques for scouting and tracking players and for finding volunteers to help with the process. Send your NT coach a message saying that you're interested in helping out and I am sure they can find something for you to do.