Not much you can do since it's a campus placement. I suffered the same way during mine, was offered a role that I didn't want and couldn't say no. So I found a different job by applying through job boards.
Try to find a job in your preferred role and just reject the offer once you do so because if the hr wants to act in bad faith there is nothing you can do as they know they have all the leverage. Startups recruit freshers, some will hire as a intern and give PPO after a couple of months. If you have time do that. It's a good way to get relevant experience for your role and easier to secure an offer that way.
If you are forced to join then keep trying for an internal transfer from Day 1 or keep upskilling through the company resources and seek opportunity elsewhere.