This choice is made during character creation. A human PC can either take the "standard" +1 to all six abilities, or I've allowed the variant: +1 to two abilities, a skill or tool proficiency, and a feat during character creation.
The ability boosts at various levels are not affected by this choice, and proceed as usual. I won't be using feats during the course of the game, so taking the human variant feat is a once only choice during character creation. Also, note that your PC will be starting at 2nd level, so you can also weave any of those choices into your PC.
Part of the reason I'm using the stripped-down basic rules is so there is no need to "buy in" with the Player's Handbook, or any other barrier to entry for anyone who wishes to join the game. Plus, the module was originally written for Classic/BECMI/RC D&D, and 5b really evoked that same "feel" when I read through it.
As such, if you don't have the Player's Handbook to make a feat choice, please let me know (here, or via PM) and I'll hook you up with a list.