I have career gap after bachelors degree and irrelevant work experience. How do I write SOP for MS admission in US?
Unlike employers in industry, I believe that graduate admissions committees don't care if there are gaps, irrelevant work experience, or changes of direction in your employment.  Their sole concern are your credentials and capabilities to do academic work.  You should focus all your attention on communicating your skills and capabilities to do Masters-level Computer Science work.  This includes your course grades as an undergrad, your GRE scores, your computer experience in industry, your recommendation letters, and your engagement with professional and academic communities.

(Business schools are probably an exception to this.  Work history is probably important to getting accepted in an MBA program.)