Use assertive body language. Face the other person, stand or sit straight, don't use dismissive gestures, be sure you have a pleasant, but serious, facial expression, keep your voice calm and soft, not whiney or abrasive. blaming the other person.

Can you be assertive and be respectful at the same time?

An effective communicator is assertive and respectful at the same time. They present their ideas with confidence and conviction. They seek to make others understand their point of view. But, no matter how passionate and ardent they might be, they don't resort to hostile, belligerent or antagonistic communication.

How can I be polite but assertive?