Hi Namita, I received both of my big 4 internships offers from an off campus route so the answer to your question is achievable. You can start by reaching out to people already working in your target company. I followed a lot of people in the companies I wanted to intern at in order to stay updated with any job openings. You can also apply on their portal for any opportunity. However, getting to know about the opportunity works best through a strong network, as per my experience

Having previously received three big 4 offers for an internship, my view would be specific to their recruitment. Getting into the Big 4s is not that hard. Try to be familiar with the background of people that they recruit. Your preparation would largely depend on the division you plan on getting into. Once you are confident, reach out to a number of individuals on LinkedIn and let them know why you would be a fit for their team…. Getting into the MBBs (and strategy arms of Big 4) is extremely difficult mainly because of how selective they are. You would be required to have a stellar academic background and a solid internship/work exp. in order to land an interview call at the firm. The networking part would still remain the same. Best of luck