Start the Mission Data Hive - Rally Point Echo(5)

You should be here on spawning in:


Jump down onto the bridge below:


I find the RNG better by going LEFT of this pillar, but either way is fine...

Just hug the wall and sneak up behind the Chieftan in the middle and get an easy 1-hit backstab


Then all you have to do is reload the checkpoint...you'll get the challenge in no time!