If you know you won't be able to make the payment, contact the bank before the due date, not after you've accumulated arrears.
Steps
Explain the reason and ask about the official alternatives available, such as rescheduling or deferring payments according to the bank's policy.
Ask about the impact of each option on the payment, the loan term, and the total cost.
Don't rely on a verbal promise, and don't stop payments on your own, as late payments can negatively affect your credit history.