Is it permissible to work in the credit department of a bank for one year, knowing that it is a forbidden job, and then move to another permissible department afterwards, in order to avoid losing the job entirely?

If a bank is usurious (Riba-based), then working in it is forbidden in all its departments, not just in the credit field, due to the generality of Allah's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."

You must leave forbidden work immediately, unless you find an urgent necessity that permits you to stay temporarily, while diligently searching for permissible work. And remember that whoever fears Allah - He will make for him a way out and provide for him from where he does not expect.