Got an offer in tcs ninja role

2 days before, I got the offer letter from tcs regarding the Ninja role with 3.4 lpa salary. I'm not sure what to do, I have heard people take this as a backup option, but I don't want to get in any legal troubles so I wanna ask that if I accept the offer today, during the joining letter or in the mean time, can I revoke my acceptance and decide to not join instead?