Hey! Fellow bad player here (currently LVL 28) and I've seen some posts asking for a guide on stirrup but all the comments are all "rush office" and doesn't really help in any way so I thought I'd contribute a bit
I had a good bit of trouble last wipe with this quest. I've concluded that there are 2 ways to do it (I did it within ~2-4 tries with the second method):
1) This is the obvious one and what I did last wipe: If you like task speedrunning with pistols, just keep playing and eventually you'll get 3 kills while doing a pickup or a marking quest
2) This is the fastest way to get it done: Load into a factory (maybe pack some armor or helmet, painkiller is a must for me), don't cheap out on the pistol (I recommend the P226R barter from peacekeeper LL1, if not, the Glock 17 from mechanic LL1 or the Granch from prapor LL1 are also good options. Don't buy the cheapest 9x18mm ammo, do your research!).
When you spawn in close to the office area, run into the second floor showers, close the doors and wait. When you hear a good amount of gun fire upstairs, rush up and try to get the pick. You can also do this with the jaeger PMC headshot tremor task by dehydrating yourself with croutons from therapist (personally I did it with this task since tremor is not too bad at close range). Also remember to hold your breath when shooting at someone unaware
If you spawn too far from office, keep a vigilant eye and try to not play too aggressive/be in a hurry to get into office. it's always better to spot someone and gauge if you can take the fight first instead of shooting at some chad with an alytn. Just slowly make your way to office while trying to get picks in the mean time
Lastly, just because this is the fastest way (imo) to do the mission and that I did it in very few tries doesn't mean it's easy! It's just the most consistent method since I used the second method on my 6 PMC kills in factory; which still took me 5-6 tries to get it
Good luck rats, don't hesitate to PM me for any more help