On the Duty Officers tab, there is a tab along the side called "Passengers" where your Colonists live. To turn in Resettle you will need to have space for at least five. I would recommend putting on the Exchange enough Colonists to make that space (or, alternatively but less profitably, just Dismiss them for Dilithium Ore).
Or find a 'Relocate Colonists' or 'First-In Colony' mission, which is what those colonists are for. Dil rewards are pretty good on those, really good on a crit. Of course that means you'll have to wait a few hours for that mission to complete (and use up those colonists) before you can accept the new colonists waiting in your completed project queue, but what's a few hours?
Personnel trading and contract sale isn't quite the same as human trafficking. You see it all the time between sports teams, corporate divisions, etc. It's pretty common in military fiction and history - not so much in modern practice but it was part of naval tradition for a long time, and particularly common in eras like WWII where it often fell to lower ranking soldiers to cobble together working units in the field. The person themself is not being traded, only their job. Hence why officers are viewed as dossiers.
Edit: Holy cow this is an old necro thread. Whoops, kill it with fire.