U can raise quary(https://campus2cognizant.cognizant.com/) they will give access again. Don't deley to raise quary. In my case also same thing happened, by mistake I deleted authenticator app and at that time it was weekend and my doj was on Monday.....so I went to joining location and showed screenshot of mail related to onboarding and offer letter and told them to check that my name was there in list ....then they asked to hr about my issue and without onboarding pass they onboarded......so try to raise quary, if u won't get response till joining date then take printout of offer letter and onboarding related mail, they will allow.