When you make your way to get a coffee in the waterworks section, Haldo will be in front of a warp gate, after a convo, you’ll find that he’s fallen on hard times, initially you’ll give him some currency. But for this achievement, you’ll need a candy bar.
Luckily there’s a merchant that is around the area that sells candy bars, look for a shopping trolley icon, buy one from him, and give it to Haldo. He’ll thank you, and the achievement will unlock.
Edit: Make sure you do this the first time you meet him, as it appears that you'll only have a limited amount of time to do this task. Thanks @mickos for the tip