بسم الله الرحمن الرحيم
What is the system of CITI Bank? What do you mean that it is on its process? What is the main business of the company? You should have mentioned all these things.
However, if your duty is not to do interest based calculation or helping it and you have not to commit any other unlawful things then it is lawful for you to work in the company.
But if the job involves any unlawful thing then mention it and submit your query again.
Allah knows Best!
Darul Uloom Deoband