In the future, to post on this forum, you must first satisfy two requirements.
1. You must own a chain whip and a lockring tool.
2. You need to be able to the demonstrate the basic logic of torque and how to screw and unscrew threaded objects.
But seriously...never trust shop people to install your cog and lockring correctly, because unless then are fixed gear knowledgible, they will fail. Its worth learning how to do it yourself....the tools are cheaper than a new hub+cost of wheel rebuild.