To soothe or calm someone (or an animal) — to pacify an angry or upset person using words or actions.
母は泣いている子供を優しくなだめた。
The mother gently calmed the crying child.
上司が現場のスタッフをなだめて状況を収めた。
The boss calmed the staff on site and brought the situation under control.
犬を叱るのではなく、まずなだめてからしつけると効果的だ。
Rather than scolding the dog, it's effective to soothe it first and then train it.