بسم الله الرحمن الرحيم
A job in bank wherein one has to assist in taking, giving interest or writing interest or bearing witness to it, is not lawful. The Holy Prophet Muhammad (may peace and blessings of Allah be upon him) cursed those who take interest, give interest, write it and bear witness to it. (Mishkat: 244)
A bank manager has to sign interest based documents hence this job is not lawful. Try to find out any other lawful job and as soon as you find one leave this job.
Allah knows Best!
Darul Uloom Deoband