Hi everyone! Thanks for all the feedback!
I believe most of you are having the same issue, which is the button not appearing when you select a settlement. There are two possible causes: a good one and a bad one.
The good one is you just haven't found the right settlement (not all of them have buttons). There should be about six settlements spread throughout the map, and the one that spawns workers lies in the top-left corner. You can explore the map by dragging the screen with the middle mouse button. If this is the case, it's obviously my fault for not leaving any explanations for the controls anywhere >.<
The bad one is that it really is a bug, which I'm searching for but am failing to find. If possible, could any of you attach a screenshot of, say, the training camp selected but not showing any buttons?
Thanks again for all the comments!