https://www.fanbyte.com/guides/destiny-2-braytech-transponder-scanner-buff/ Here's another guide that I think is pretty thorough. Once you purchase the transponder, you have to go to the eclipsed zone and find the fallen with the scanner buff. It's a bit of a pain to kill because you have to kill the enemies right around it first (mostly shanks and servitors) and it frequently spawns exploding shanks, but it doesn't regenerate or anything so it shouldn't be that hard to kill in a few minutes. Once it's dead, if you have the transponder, you should be able to pick up the scanner. Then you should see text on the left side of your screen saying “Scanner (Riis-Reborn Sector) x3.” In that sector, find sets of 4 drones, and kill whichever one is yellow until all 4 are dead. Then there should be a targeted object very nearby to interact with. This gives you an item drop (nothing fancy), and after you've done this to all 3 sets of drones in the sector, you get the triumph completion.