The crashed Venator is on Zeffo. In the Crash Site area where you are swimming and come upon a Jotaz that is fighting a number of Scazz, you start climbing on the wreckage. You need the double jump so you can reach the entrance on the right side of the area. Follow this area through to the end and you will find a room with 3 chests in it and a Jotaz fighting a couple scout troopers. When you step outside to collect the gold chest that contains a stim upgrade, you will unlock the achievement.
EDIT: So it seems that many people are having trouble getting this achievement. I didn’t do anything special when I got the achievement so I don’t know exactly why It isn’t unlocking for some but is for others. Only thing I could recommend would be to fully explore the ship 100%. I did this naturally which could have been why I got the achievement as soon as I reached the chest room.