I got into FTE in cognizant and selected for TCS Digital

I got into FTE in cognizant and selected for TCS Digital, I don't know when I will get joining in TCS, should I get converted into FTE In Cognizant?? The problem is if I get converted to full time in cognizant, I should create a UAN number, will it affect tcs in the bgv process? Also notice period in cognizant is 3 months which would be tough during resignation if I get joining from TCS. And also, what if I don't get joining in TCS till another 4 to 5 months. Kindly suggest a solution for me.