Trending @Cognizant; Switch to Big 4

Hi, I am currently working as a data engineer in cognizant. It is my first company. At joining I was tagged to a project as data engineer with ETL developer role. The project used some old legacy technologies and as the offshore team was small, we had to do all the associate level works since when we were PATs, but the salary was of course of PAT level and no extra monetary perks were provided. The only pros were you had all the prod level accesses, you could directly have calls with client so exposure was of senior level and perhaps it’s the only project with on-site opportunity as soon as you become PA. So in my case my onsite processing was started when I became PA & my visa processes were started by Cognizant. But due to some finance conditions, the client cut down the offshore employees and eventually we got released. Now I am more focused to develop modern data engineerings skills as my current work experience is of 2 yrs & now I want to switch to big 4 companies. Can anyone pls guide me??